Science on the Case

BALLISTICS DATABASE


Two years ago, a security guard was murdered in Houston and a .40 caliber Smith and Wesson cartridge was found at the scene. Earlier in the day, two store clerks were killed during a robbery and three .40 caliber Smith and Wesson cartridges recovered. By comparing the extractor marks on cartridges from both incidents, the police ascertained they came from the same gun.


The police then turned to the National Integrated Ballistic Information Network (NIBIN), a database of information about the weapons used in thousands of crimes committed in the United States since 1993. They instantly found a match between the marks on the recent cartridges and those on a comparable one that had been discovered after a man was robbed at gunpoint in Houston earlier in the year. The detectives also learned from the database that in the earlier case, the thieves had tried to use the victim's credit card at a convenience store. That robbery was initially considered too small for an in-depth investigation, but now that a murder had been committed the police questioned the convenience store clerk-who, it turned out, knew one of the criminals by name. Based on his testimony and the ballistics evidence, Gilmar Guevara, the triggerman, was convicted. Two accomplices await trial.


Houston is an early user of NIBIN, but by 2003 all state and local authorities will have access to the network. The main NIBIN unit distributed to most police departments will contain a Data Acquisition Station (DAS)-a microscope and image-capture hardware-on which authorities can enter images of weapons and ammunition as new crimes occur. The database is expected to grow by thousands of cases each year.


PORTABLE CHEM LAB


The Forensic Science Center at Lawrence Livermore National Laboratory in California has designed a portable device that breaks evidence down to its chemical components and, within an hour, unmasks critical aspects of a crime-right at the scene. This 61-pound, suitcase-size device-a miniature gas chromatograph- mass spectrometer (GC-MS)-can tell a person's age range and gender from secreted hormones in a fingerprint smudge. It can reveal the presence of drugs such as cocaine or heroin from a single crystal smaller than a grain of salt. It can compare the ingredients of the glue in duct tape used to bind a victim with comparable ingredients from tape found in a suspect's car. It can analyze a handwritten or computer-generated letter to characterize the type of ink or toner used.


The sample is collected by dabbing material or waving a probe in the air. It's then inserted into the GC-MS's heated chamber, which vaporizes it into an aerosol and passes it through a column to a mass spectrometer. There the sample is hit with an electron beam that breaks its molecules into individual ions that are unique to its chemical makeup. The GC-MS compares the results against a database of over 100,000 compounds to identify the chemicals present.