Lasers, polymers, computers: high tech fights crime

In New York City on May 19, 1911, Caesar Cella, alias Charles Crispi, was convicted of burglary because the ridges of his fingers formed an impression that matched prints found at the scene of the crime. It's the first known instance of fingerprints being used as evidence in a trial.

Today fingerprints are small guns in the expanding arsenal of technology that courts and law enforcement officials are employing to combat crime.

From analyzing traces of gunpowder with electron microscopes and X-ray diffraction, to uncovering ''invisible'' fingerprints with special lasers, to matching voices with computers programmed to recognize speech patterns, the art of forensic science is altering traditional means of law enforcement.

Courts are still struggling with the question of admissibility of some of the evidence gathered from the new gadgets, but ''the trend is to more technological evidence than has ever been admitted in the past,'' says Gerald Uelmen, law professor at Loyola Law School in California.

Nearly half the judges and attorneys surveyed in a recent study by the National Center for State Courts said scientific evidence was being introduced in about one third of the cases they processed - almost no such evidence was used 15 years ago.

Scientists are now able to determine a person's race, sex, and other characteristics from a single strand of hair. In arson cases, a new polymer called Tenax can be used to detect as little as one millionth of a liter of gasoline. Even footprints are becoming accepted as a means of identification.

Other older technologies have been highly refined. The biggest leap in knowledge has been in identifying new blood types. For years scientists confined their work to four main groups, but now more than a dozen have been identified. In handwriting analysis, a new machine can distinguish between near-perfect matches.

Many of the technological advances are controversial, especially those which are normally coupled with a pyschologist's interpretation of the data collected. The Massachusetts Supreme Judicial Court Sept. 8 prohibited the use of lie-detector tests as evidence in trials.

Those supporting the increased use of scientific evidence point to the Atlanta murder conviction of Wayne Williams, in which a weak prosecution case was bolstered with scientific evidence linking carpet fibers and blood stains found near the victims to Mr. Williams.

Two factors have hastened the development of forensic science. First, the technological explosion of the 1970s produced a flood of new crime-fighting devices. Second, courts have for many years been tightening ''exclusionary rules'' for the admission of evidence. Many prosecutors say the rules created a vacuum of physical evidence that only technology could fill.

But not everyone is sold on the virtues of the new machines. ''Technology will never replace human investigation,'' says Wiley Thompson, supervisory special agent for the FBI.

While the technology results in ''more reliable fact-finding, it could be misused if prosecutors and defense attorneys don't take the time to learn about existing techniques and to keep witnesses honest,'' says Edward Imwinkelried, law professor at Washington University in St. Louis.

He cites results of the federal Laboratory Proficiency Testing Program of the mid-70s, in which evidence produced in crime labs proved inaccurate in up to half of the cases studied, due to human error.

The standard for acceptance of new technologies in the courtroom is the ''Frye test,'' based on a 1923 decision. The ruling - prohibiting courtroom use of any technology that is not generally accepted in the scientific community - was designed to ensure that there is an adequate pool of experts familiar with the technology who could be called on to testify.

But that definition is too vague for some judges, who oppose the Frye test, saying it excludes too much relevant evidence.

Prosecutors, too, often feel compelled to support their cases with scientific evidence. ''It convinces jurors most,'' says George Dell, a superior court judge in Los Angeles County, ''and if it isn't presented, they'll ask why it hasn't been.''

Professor Imwinkelried says experts are ''taking a long, deep breath, looking at what we have, and trying to figure out concrete, reliable technological standards.''