INFRARED: AID TO LAW ENFORCEMENT

BY J. EDGAR HOOVER

Three young children of a family living in a western state died mysteriously within a short period of time. The death of the third victim, a baby girl two and one-half years old, aroused the suspicions of authorities. In connection with the ensuing investigation, an autopsy was performed and the major body organs of the little girl were submitted by local law enforcement officials to the FBI Laboratory for examination.

From 200 cc of the distillate obtained from a steam distillation of the child's organs, FBI Laboratory technicians were able to isolate, by extraction with 1 cc of chloroform, approximately one-third of a drop of an oily liquid. This unknown oily liquid was subjected to examination and analysis in the infrared spectrophotometer and was identified as methyl salicylate after a study of the infrared spectrogram. Methyl salicylate is a volatile poison commonly known as oil of wintergreen. Due to the extremely small amount of liquid available for examination in this and similar cases, it is doubtful if normal organic identification techniques would have been effective in identifying the compound.

The facilities of the FBI Laboratory are available, without charge, to all authorized

law enforcement agencies throughout the country. Specimens of evidence are forwarded to the Laboratory for examination in connection with every type of criminal case. Specimens examined in which infrared analyses have played an important role include drugs, poisons, plastics, rubber products, waxes, petroleum products and many other frequently used organic products.

Two of the major problems confronting the Special Agents of the FBI Laboratory are the identification of an unknown substance and the comparison of two or more specimens from different sources. These problems are complicated by the fact that evidence unintentionally left by a subject at a crime scene, or deposited on his person or personal effects while he is at a crime scene, by its very nature is normally extremely limited. Such evidence is also frequently contaminated. The majority of items analyzed are not chemically pure samples but are, rather, in the form of finished, commercially available products. In this regard, known spectrograms, along with collections of drugs, rubbers, plastics and paints used for reference purposes, have proved to be invaluable aids in the interpretation of infrared spectrograms and the subsequent identification of unknown substances.

An infrared spectrophotometric examination played an important role in a recent case involving theft of government property. Supplies were being pilfered at periodic intervals from a military warehouse in a southern state. In an attempt to trap the thief, authorities carefully and sparingly dusted items in the warehouse stock with an organic fluorescent powder. Subsequent to the dusting of the items in stock, several suspects were examined with the aid of ultraviolet light. The shirt and hands of one of the men exhibited a telltale glow.

The shirt of the suspect was forwarded to the FBI Laboratory with a request to identify the foreign fluorescent material on it and for a comparison of that foreign material with samples of the known fluorescent dusting powder.

Although the foreign deposits on the shirt appeared to be very abundant when viewed under ultraviolet light, the amount extracted, concentrated and available for examination was very minute. An infrared spectrophotometric examination of this powder enabled the FBI Laboratory examiner to identify the powder as similar in composition to the powder which had been dusted on the stock in the warehouse. The suspect was brought to trial and pleaded guilty to the charges against him.

The infrared spectrophotometer supplements the spectrograph, visible spectrophotometer, X-ray and electron diffraction units of the FBI Laboratory. The majority of these instruments measure, by nonconsuming operations, many of the characteristics of the most minute amounts of evidence. The characteristics observed from the instrumental and microchemical analyses are interpreted, compounds are identified, and materials found at the crime scene and on the person of the suspect are compared. The results of such identifications and comparisons lead to an understanding of the evidence, yield extremely useful investigative leads, and constitute valuable evidence for use in a court trial.


Perkin-Elmer Model 21 Infrared Spectrophotometer plays a role in crime detection at FBI Laboratory in Washington, D.C.