forensic science - Christie's Mysteries

Witnesses for the Prosecution: Forensic Science During Agatha Christie’s Life

Posted on September 19, 2021September 19, 2021 by Harley

Agatha Christie (1890-1976): Polymath and Natural Scientist

Agatha Christie was born in September 1890 and lived through 1976, so her work was inspired by and utilized the concepts of forensic science that were established during this time period.

Christie had no formal education during her upbringing but was a polymath and a natural scientist. Her father taught her arithmetic, and she had an inherent understanding of quantity, scale, and proportion. She also taught herself to read and read a range of books and newspapers throughout her life, including the Daily Mirror and the Telegraph. Examples of forensic science in action from these newspapers are shown below to illustrate what Christie was exposed to.

Foundations of Forensic Science

The earliest written accounts of the use of forensic science were in 6th century China. The term “forensics” comes from the Latin “forensis,” which means “of or before the forum.” The primary definition of “forensic” is belonging to, used in, or suitable to courts of justice or to public discussion and debate.

Forensic science, the focus of this post, refers to the application of scientific principles and techniques to matters of criminal justice especially as relating to the collection, examination, and analysis of physical evidence. According to the Canadian Society of Forensic Science,

Forensic science is therefore the application of science, and the scientific method to the judicial system. The important word here is science. A forensic scientist will not only be analyzing and interpreting evidence but also challenged in court while providing expert witness testimony.”

Criminalistics refers to the specific scientific tests or techniques that are used in connection with the detection of crime. Criminalistics is a subset of forensic science and started with the “scientific aids” movement in the UK. An example of criminalistics would be the collection of fingerprints at the scene of a crime by a CSI technician, which are then examined by a forensic scientist with an expertise in fingerprinting.

Forensic Science and Agatha Christie at the Turn of the 20th Century

At the turn of the 20th century, around the time that Agatha Christie was born, the field of forensic science had evolved to suit the need to present evidence in a courtroom, which was (as it is now) primarily done through expert witnesses. The earliest types of witnesses were medical experts, such as a doctor testifying as to the cause of death, but by the end of the 19th century, other scientific fields were beginning to be represented.

Below is an example from the Daily Telegraph from the Dreyfus trial in 1899 detailing the testimony of a handwriting expert. This was Captain Alfred Dreyfus’s second trial for treason against France, and he was erroneously found guilty based on this expert handwriting analysis. The case is an example of the theoretical nature of many areas of forensic science as well as the influence that the media has in portraying forensic science as a single source of truth. The case was also an example of unchecked antisemitism, which was also present in Christie’s early works though lessened as she matured as an author and a human. Dreyfus was subsequently pardoned and served in World War I.

At this time, a few forensic science techniques were already widely accepted, most notably fingerprinting analysis. One of the first celebrities in forensic science in the UK was Bernard Spilsbury, a Home Office forensic scientist. His authoritative performances in the witness stand, for example at Crippen’s trial, were held as an example until the 1980s. But his celebrity status led the public to conclude that forensic science would provide absolute, unquestionable proof.

Spilsbury gave compelling evidence based on his microscopic examination of human remains recovered in Crippen’s home that a scar on a piece of skin identified the remains as those of Crippen’s wife, whom Dr. Crippen killed and then escaped with his mistress via ship to Canada.

The Crippen case was among the first true crime cases to receive full media coverage complete with descriptions of recent scientific advances such as the wireless telegraph. Christie would have read about the case and its trial, and even used it as inspiration for the historical crime in the 1952 Poirot novel Mrs. McGinty’s Dead.

Also in the 1910’s, Christie began volunteering as a nurse and may have chosen nursing as a career, if she had not become a successful writer. But many of the best scientists are inherently creative, and Christie had a keen interest in science throughout her life. She also married science with her creative writing, for example with her poem “In a Dispensary.”

She transitioned from nursing to dispensing (also known as pharmacy) during World War I. As part of her training, she learned chemistry and physics and kept notebooks listing various substances (their appearances and properties) in alphabetical order.

In 1917, she passed 2 of the 3 parts of the Society of Apothecaries’ examination: chemistry and medica (composition of medicines). She passed the practical portion on her second try.

Forensic science to address criminal poisoning cases developed early in natural history, as early as the mid-18th century. In the mid-19th century, the Society of Apothecaries began to require their candidates attend lectures in medical jurisprudence. At this stage, a doctor could harvest samples and organs for testing for the presence of poisons.

Christie’s knowledge from her dispensary training was most applicable to the study of poisons and toxicology. More broadly, analytical chemistry was widely used for extracting metals, manufacturing synthetic dyes, and conducting quality control. Analytical chemistry is an area of applied science that answers the questions about an unknown substance: what is there and how much exists.

The Institute of Chemistry was founded in 1877 in the UK, which formalized the field of analytical chemistry. Additional formality to scientific careers was introduced in the early 20th century when the Department of Scientific and Industrial Research was established following World War I.

Christie used her knowledge of poisons to craft her first mystery novel, The Mysterious Affair at Styles, around 1916. The book was not accepted for publication until several years later. In the original draft of the novel, Hercule Poirot revealed the solution while serving as an expert witness in a murder trial, showing Christie’s knowledge of the forensic application of science.

The Relationship Between Mystery and Science

The transition from practical science into mystery writing was a natural one. Essentially, science seeks to solve the mysteries of the universe. Below on the left, this diagram shows the Scientific Method, which is the accepted stepwise process for conducting scientific endeavors. After making observations, a scientist poses a question, which is answered by a hypothesis. A hypothesis is a statement about the question that can be disproven or rejected. The scientist then conducts experiments to test their hypothesis. Once the experiments are complete, the scientist can reject or fail to reject their hypothesis, which leads to a conclusion to their question. It may not be the answer, but it will provide information hopefully leading to the answer eventually. It is a cyclical process that repeats ad infinitum.

Below on the right is a similar diagram showing the structure of a mystery story. Of course, stories can vary in their presentation, but generally every mystery story has a central crime. After the crime has occurred, a detective or other character collects clues to inform a theory of what has happened. When the detective is confident in their theory, there is a confrontation with the criminal. And like science, when the theory is tested, there is a conclusion to wrap up loose ends in the story and perhaps point to future stories.

Christie was not the only author to transition from medical sciences into mystery fiction. Sir Arthur Conan Doyle, the creator of Sherlock Holmes, was a physician, and Richard Austin Freeman, the creator of Dr. John Thorndyke, was educated in medicine. But Christie distinguishes herself with her breadth of knowledge specifically regarding poisons

Forensic Science in the 1920s Through 1940s

The following decades were a period of growth by Christie the author and also in the field of forensic science in the UK. Detectives with Scotland Yard had acknowledged that more knowledge and coordination were required to detect and apprehend criminals. Below is an overview of the key forensic scientists and developments during this important time period, as Scotland Yard worked to incorporate forensic science to solve crimes.

Hans Gross

Toxicology may be the first true forensic science, as the field developed in the 19th century specifically to be used to solve crimes. Somewhat later, crime scene analysis was developed by Hans Gross in his Handbook for Examining Magistrates. His work was practical and addressed how to manage and preserve evidence from crime scenes. However, his work was marred by frequent references to the Romani as criminals. When his handbook was first translated into English, it was done so in the British colony of India and transposed these racist beliefs onto the native tribes. Eventually, newer editions of the work edited out these racist segments. The importance of Gross’s work was its reliance on the materials at a crime scene that could be properly collected and serve as objective “witnesses” to a crime. Crime scene analysis inspired by Gross’s work was adopted by Scotland Yard in the 1930s.

Cesare Lombroso

Cesare Lombroso measured and categorized an untold number of skulls in the hopes of quantifying criminality. His work was translated into English in 1927 and introduced the notion of a “born criminal” that could be identified through physiognomy, and examples are shown below on the right. It was never fully accepted in the UK, likely due to Lombroso’s reliance on theory rather than empirical science.

Alphonse Bertillon

Alphonse Bertillon created the Bertillon System, an anthropometric approach to measuring criminals and criminality, in 1879, but he also pioneered crime scene management and forensic photography. Bertillon developed precise photography techniques of the face and profile of criminals, and his photographic techniques were applied to crime scenes as metric photography, which used physical measuring scales (such as rulers) to provide a permanent and accurate record of the crime scene including the location and size of objects. Although fingerprinting ultimately proved superior to anthropometry in identifying criminals, the 2 techniques were used in concert for many years. And of course, the mug shot technique developed by Bertillon is still in use.

Juan Vucetich and Edward Henry

Fingerprinting for criminal identification was first used by Juan Vucetich in 1891 in Argentina. Sir Edward Henry developed a fingerprinting system that was adopted by Scotland Yard in 1901 and was the basis for the US FBI criminal files created in 1924. This adoption followed the recommendation by the Belper Committee of the Home Office to utilize fingerprinting alone for criminal identification. Henry’s system includes subclassification of fingerprints with more than 1024 categories and subcategories. Matches were made through manual examination of fingerprints with a magnifying glass and was therefore not useful if there was not a print in the catalogue to match to, and the system was also flawed by classification errors that could prevent the identification of a print. In the 1960s, the first computer programs for fingerprint identification were based on the Henry system.

Edmond Locard

Edmond Locard was a French forensic scientist with an impressive laboratory in Lyon that was held as an aspirational example to forensic scientists in the UK. Locard was known as the “French Sherlock Holmes” and proffered his exchange principle, which asserted that whenever there is contact between 2 items, there is an exchange of material; this is the basis of several forensic sciences such as fingerprints and fiber analysis.

Sydney Smith

Sydney Smith served as a medicolegal expert for the Egyptian government prior to his appointment as a Professor of Forensic Medicine at the University of Edinburgh. In 1924, he and his colleagues employed one of the earliest uses of ballistics to identify the gun used to assassinate Sir Lee Stack Pasha. Similar to fingerprinting, the unique markings left on a bullet by a particular firearm were evaluated using a comparison microscope.

Alfred Lucas

Another early work in the field was Forensic Chemistry and Scientific Criminal Investigation by Alfred Lucas, first published in 1920. Lucas was a British analytical chemist who had worked alongside Howard Carter in his Egyptian archaeological excavations. The book was highly detailed and a basis of forensic science in the UK for several decades. Lucas was also a correspondent of Nigel Morland, a crime fiction writer from the 1930s through the 1970s who would reference Lucas’s work throughout his fiction.

Forensic Science and the Public

The media was a primary source of information about forensic technologies to both the public and criminals. Alfred Lucas stated in Forensic Chemistry, “

...in fact the criminal is becoming so scientific, not only in his work, but also in the means he adopts to escape detection, that a scientist is needed to cope with him, that is to say, a scientist must be set to catch a scientist.”

As early as the Victorian era, there was considerable public interest in crime reporting. At the turn of the century in the UK, the creation of tabloids capitalized on this appetite. The reporting of the Crippen case offers the best study of the role of the press in disseminating knowledge of criminals and forensic science. Most notably, the use of the wireless telegraph in apprehending Crippen was so widely described in the media that scholars have suggested

the Crippen saga did more to accelerate the acceptance of wireless as a practical tool than anything the Marconi company had previously attempted.”

The Departmental Committee on Detective Work for England and Wales

In the 1930s, the Home Office commissioned the Departmental Committee on Detective Work for England and Wales “to inquire and report upon the organization and procedure of the police forces of England and Wales for the purpose of the detection of crime.” Their report was submitted in 1938 and provided substantial evidence of the relationship between scientific training and analysis to the detection of crime. This allowed for the establishment of additional laboratories with the purpose of solving crimes and essentially formalized the field of forensic science.

The Detective Committee report acknowledged that the majority of crimes in the 1930s were against property and not people. Violent crimes (including sexual crimes) comprised about 2.5% of all crimes, violent crimes against property about 19.5%, nonviolent theft about 75%, and forgery about 1%. Burglary and breaking and entering crimes had tripled since the beginning of World War I. The report also acknowledged the ability of criminals to move location and evade detection, and so recommended the centralization of records as well as maintaining adequate local police forces. The Detective Committee report estimated that 4% of crimes (>10,000) would require scientific analysis of evidence.

Around the same time, in 1935, the Metropolitan Police opened its first forensic science laboratory in Hendon. However, it initially struggled to work in concert with the police force, and little work was forwarded from Scotland Yard. Coordination between police officers and forensic scientists was a continual challenge in the UK, as there were often class and educational divides between the 2 professions.

In 1946, a public education campaign released a film entitled Science Fights Crime to announce the resumption of detective training courses. The video demonstrated the newest scientific methods in forgery, fingerprinting, burglary, self-defense, identification of suspects, ballistics, and infrared and ultraviolet photography.

Scientific Aids

Forensic science theories evolved along with technology. In 1946, Sir John Maxwell, former Chief Constable of Manchester stated,

...great progress has been made in the application of science as an aid to police work. The introduction of the motor car...the use of wireless, the gradual development of police laboratories to help in crime investigation and the adoption of traffic signal lights are typical examples of the process of mechanization.”

This was the era of “scientific aids” in policing.

Throughout this era, “scientific aids” were developed and promoted for use by police officers. These are roughly equivalent to “criminalistics” and were to be used by police officers during their investigation of crimes to help allow for objectivity in the processing of crimes. An instructional pamphlet published in 1936, Scientific Aids to Criminal Investigation, provided highly detailed descriptions for what to do at a crime scene. There were several parts to this publication, a few of which are shown here.

The goal of scientific aids can be described by the following quote:

Scientific evidence, when properly interpreted, may thus provide, in certain classes of cases, a kind of proof which never lies and never alters its tale, and which, if placed before the Court by a competent witness, can be seen by Judge and jury for themselves.”

Forensic Science from the 1950s Onwards

As with many other fields, the development of forensic science paused during World War II, which stagnated scientific advancement for many years. According to author Alison Adam, “the development of the forensic science profession was complex and piecemeal.” The forensic science principles described in this presentation continued to be used throughout the remainder of Agatha Christie’s life, with few notable breakthroughs until the mid-1980s with the advent of DNA identification.

Crime fiction evolved along with criminals and forensic science, and Alison Adam posits that both science and crime fiction strove to establish and maintain social and moral order at the turn of the 20th century. Agatha Christie had a strong interest in criminology and forensic science throughout her career and stated in her autobiography,

As a result of writing crime books one gets interested in the study of criminology. I am particularly interested in reading books by those who have been in contact with criminals, especially those who have tried to benefit them or to find ways of what one would have called in the old days ‘reforming’ them–for which I imagine one uses far more grand terms nowadays!”

Night Train to Perdition, Act III

Posted on May 31, 2020April 30, 2021 by Harley

See Night Train to Perdition, Act I, for a summary of Murder on the Orient Express, and Night Train to Perdition, Act II, for a summary of related true-crime cases, including the kidnap and murder of Charles Lindbergh, Jr. The post you are reading details the forensic science responsible for the capture and conviction of one of the kidnappers, in particular the wood evidence provided by the ladder used in the kidnapping.

The Wooden Witness

As noted in Act II, two key pieces of evidence were discovered immediately following the crime at the Lindbergh estate: a handwritten ransom note and a custom ladder. In their preliminary examination of the three-sectional ladder, the investigators postulated that the user was neither too tall nor too short and was left handed. The left handedness of the user was based on the pattern of saw blade cuts in the wood as well as the placement of the ladder to the right of the nursery window, which would allow the user to navigate entry into the nursery from his left side. The runners used in the ladders appeared to resemble wood crates that were used to protect bathtubs during transit, and police reported that the ladder was similar to those used with pipe organs.

However, these initial theories brought investigators no closer to an actionable lead. Dr. Erastus Mead Hudson, an independent fingerprint expert and specialist in chemistry and bacteriology proposed to examine fingerprints that may have been left by the kidnapper or kidnappers on the ladder. Instead using fingerprint powder, which was the custom practice at the time, Hudson used silver nitrate (AgNO₃) to identify prints. Unfortunately, the ladder had been handled so extensively since the kidnapping that there were approximately 500 latent fingerprints present, which could not be used to identify any criminals.

Silver nitrate interacts with salt deposits found in human sweat and shed with fingerprints, which can then be visualized with ultraviolet light.

In the middle of 1932 and still at a loss for any leads, the investigators turned to the federal government for assistance. They sent the ladder, a chisel that was also found at the Lindbergh estate, and a soil sample to the Department of Justice. Drawing on the expertise within various federal departments, the DOJ sent samples from the ladder to the US Forest Service, of which 7 samples were sent to the Forest Products Laboratory in Madison, WI, a joint research venture with the Forest Service. Upon receipt, FPL Director Carlisle P. Winslow told Arthur Koehler, considered the nation’s top wood identification expert, to disregard all other projects and immediately identify the source of the wood in the Lindbergh kidnapping ladder. To do so, Koehler would apply his specialty in xylotomy, which is the art of preparing sections of wood for microscopic examination.

The Wood Expert

Arthur Koehler had established himself as a skilled xylotomist and had been serving as an expert witness in criminal trials following his promotion to the Head of Wood Technology at the FPL. He had recently testified in the murder trial of John Magnuson regarding the source of wood used by the criminal to encase a bomb, which led to a conviction. Koehler had even offered his assistance to Lindbergh after the kidnapping with a personal letter:

I read further in the newspaper about that homemade ladder left behind by the fellow who had done the crime and I grew excited. You see, that ladder, because it was made of wood, seemed just like a daring challenge.
Within a few days after that I wrote a letter to the Lindbergh baby’s father, saying I thought it might be possible to trace that ladder’s members until the wood matched up with other wood so as to compromise the man involved. Of course, I’m no Sherlock Holmes, but I have specialized in the study of wood. Just as a doctor who devotes himself to stomachs or tonsils or human vertebrae narrows down his interests to a sharp focus on the single field of his pet passion, so I, a forester, have done with wood.

He did not receive a response from Lindbergh.

Less than one week after receiving samples from the kidnapping ladder, Koehler had identified the various sources as Douglas fir, paper birch, Ponderosa pine, and Southern pine through comparisons with the FPL’s library of wood specimens. After submitting his report to the Department of Justice, Koehler wanted to continue helping with the investigation, his goal to make the ladder a “wooden witness.”

The Wooden Autopsy

In early 1933, the New Jersey State Police would take Koehler up on his offer. Koehler was given full access to the ladder, which he dismantled to perform an “autopsy.” Each rung and rail was numbered, measured, and calipered. Koehler identified the source for each piece and closely examined the components for marks made during the assembly of the ladder. As relatively few sources of wood were used to construct the ladder, Koehler concluded “that the maker had a limited amount of material to choose from.”

Among all the pieces of the kidnapping ladder, Rail 16 seemed to offer the greatest potential for confirmatory evidence to match to a criminal. Rail 16 was North Carolina pine (the same as Rails 12 and 13), but it was more knotty and had not been machine planed. Rather, it had been hand-planed on both edges, leading Koehler to believe that the rail was worked down from a wider piece of wood:

Why he planed both edges of rail 16 is a mystery unless it was rough edged to begin with. The edges were not always at right angles to the face, and scratches made by the plane wobbled back and forth along the edge…the scratches left by a hand plane on both edges of this rail were exactly the same as those on one side of each of the [cleats], proving conclusively that they were made by the same plane, and presumably at approximately the same time, probably when the ladder was made.

Furthermore, Rail 16 had four nail holes that had been made by square-cut or 8-penny iron nails, which had been phased out of production by the end of the 1800s in favor of cheaper wire nails made from soft steel. In the 1930s, square-cut nails were still used in home construction, and the regular spacing of the nail holes in Rail 16 suggested they may have come from a building.

Keen to pursue multiple avenues of investigation, Koehler also fully characterized the marks from the machine planer used on Rails 12 and 13. He sent letters to the known manufacturers of wood planers to inquire as to which mills they may have sold the characteristic planers, and then solicited the mills for samples for examination. From April to September 1933, Koehler sent a total of 1596 requests and received 23 samples. Despite the small number of samples, he was able to identify Rails 12 and 13 as having been planed in a mill in South Carolina by examining the planer knife marks microscopically and measuring the marks to 1/100th of an inch. Ultimately, Koehler was unable to trace the kidnapper(s) based on Rails 12 and 13 because the Bronx lumber yard from which it was likely sold was a cash-only business.

Meanwhile...

At the same time that Koehler was examining the wood of the kidnapping ladder, the police were actively tracing the ransom money. The $50,000 that was paid on behalf of the Lindbergh family by the go-between John Condon primarily comprised $20 and $10 gold certificates. Elmer Irey, an IRS accountant, proposed this mechanism to allow for easier tracing of the ransom money as the gold certificates were being phased out of circulation. The remaining ransom money was $5 bills with red seals and red serial numbers. All of the ransom money was printed in 1928, and a list of the serial numbers was sent to banks across the country.

Bills from the lot of ransom money would occasionally surface over the year and a half following its payment in 1932, most often in New York City. On 17 Sep 1933, a man paid for 98 cents of gasoline with a $10 gold certificate at a gas station in Manhattan. The station manager questioned the legitimacy of the bill and wrote down the man’s license plate number in its margin, in case the bank refused to deposit it. The manager questioned the customer about the bill, who was reported to reply, “I have a hundred more just like it.”

The license plate number was traced to Bruno Richard Hauptmann, an unemployed carpenter who was pulled over for a search shortly after leaving his house in the Bronx. When detectives found money in his wallet with serial numbers matching the ransom money, he was arrested.

The Wooden Key

Upon hearing of Hauptmann’s arrest, Koehler suggested that investigators take note of any lumber in his house that may have been used for Rail 16 as well as for any woodworking tools. In their first search of the house, investigators found a total of $13,750 of the ransom money and an automatic revolver concealed in wooden 2×4’s in the garage; they also found a large wooden plane with a nicked blade that could have been used in the construction of the ladder.

At the time of Hauptmann’s arrest, a news article reported that he once worked odd jobs at the National Lumber and Millworker Corp in the Bronx, where Koehler had traced Rails 12 and 13.

During a second search of Hauptmann’s attic, the investigators noted that the flooring comprised 27 pieces of 1×6 North Carolina pine. The final board on the south side was not the same length as the others, and they were able to discern that a piece approximately 8 feet long had been removed, leaving traces of saw marks and saw dust. A sample of the remaining board and the nails that had been used to connect the board to the joist were provided to Koehler for comparison.

Koehler observed nicks in the largest knife of the plane recovered from Hauptmann’s house that produced marks exactly matching those on Rail 16 and the pine rungs of the ladder. He concluded, “There is no question but [that] the rungs and rail were planed with that plane.”

The nails removed from the boards in Hauptmann’s attic fit into the holes in Rail 16 precisely, which lead Koehler to conclude “the board probably was removed from some of Hauptmann’s previous work either for others or for himself.” Koehler testified before the grand jury at the Hunterdon County Courthouse in Flemington, New Jersey, to these points. Along with testimony pertaining to the ransom note, ransom money, and various eyewitnesses, the grand jury found enough evidence to indict Hauptmann for the murder of Charles Lindbergh, Jr.

Meanwhile, Koehler continued his examination of Rail 16 in comparison to the wood removed from Hauptmann’s attic. He and the investigators took Rail 16 to Hauptmann’s attic, where it fit snugly into the place of the missing board. Koehler reflected that “Such a result could not happen as a mere coincidence.” Koehler had calculated the probability of all 4 nail holes matching the joists in Hauptmann’s attic perfectly as 1/10¹⁶, and he dismissed the possibility that this was mere circumstantial evidence.

1/10¹⁶, or 1 in 10 quadrillion, is the probability of 2 people randomly picking the same word out of 110 billion average-sized books.

Finally, he compared the grain, which is the appearance of the natural rings of a tree when it has been cut lengthwise to form a board:

It is a pattern that is always varied and yet the pattern of the grain in the ladder rail and floor board matched as perfectly as if the interrupted curving lines they plotted years ago had been etched within the tree just to be a trap for anyone who dared so to misuse wood as to form it into a kidnap ladder.

Every tree within itself has written all its history. The growth in spring shows white and pithy, but in the summer the slower growth becomes, in most trees, darker tissue. This is repeated year by year, and that is why these rings seem double and confuse those who try to say a tree is such and such an age. Count the band of white and black as one year’s growth. The board end of the piece of flooring that had been robbed to make a ladder showed its rings quite clear, and so did the ladder rail. A gap of one and three-eighth inches had been trimmed off, yet the rings matched.

The Wooden Evidence

At Hauptmann’s murder trial, Koehler testified his findings regarding Rail 16, but he was challenged by one of the defense lawyers, who stated, “We say that there is no such animal known among men as an expert on wood. That is not a science that has been recognized by the courts; that is not in a class with handwriting experts, with fingerprint experts or with ballistic experts. That has been reduced to a science and is known and recognized by the courts.” The judge allowed the defense council to cross-examine Koehler to ascertain the extent of his credentials. At the end of Koehler’s lengthy exposition regarding his publications in the field of wood science, the judge confirmed he was indeed a wood expert.

Koehler provided the court with complete details regarding his examination of the kidnap ladder, in particular Rail 16’s nail holes and grain. His xylotomical examination of the wood source and grain was essential to tying Hauptmann to the ladder used in the Lindbergh kidnapping. Following the testimony, Koehler was lauded as “the only real detective (in the case)” by the Reading, Pennsylvania Times, and The New York Post wrote,

The Hauptmann trial may go down in legal history less as the most sensational case of its time than as the case which brought legal recognition to the wood expert on par with handwriting, fingerprint and ballistic experts.

After 42 days of testimony from Koehler and others involved in the Lindbergh case, the jurors retired to deliberate on the verdict of Hauptmann. Less than 12 hours later, the jury returned with a verdict of guilty. The judge passed down a death sentence to the convicted murderer of Charles Lindbergh, Jr. Koehler’s testimony stood up to several appeals by Hauptmann, and on 03 Apr 1936, his death sentence was carried out by electric chair. Hauptmann never confessed to the crime and never indicated if other kidnappers were involved.

Koehler continued working as a wood identification expert but never in so sensational a trial as the Lindbergh case. He died in his home on 16 Jul 1967 at the age of 82. Although wood evidence continues to be valuable to forensic science, it has never again been at the forefront of a crime as in the Lindbergh kidnapping.