It is hard for a defendant to argue that he wasn't at the scene of a homicide when his DNA is all over the handle of the knife used in the killing.
Decades ago, forensic scientists could not have gleaned such information from evidence. But because the homicide in question occurred in 2000, Diana Brooks, deputy state's attorney for Harford County, could read a lab analysis that put the defendant, who was later convicted, squarely at the homicide.
"There had to be some accounting of why he was there," Brooks said.
That case is a blunt statement of DNA's potential: Although DNA might not absolutely identify someone as guilty, it can place someone at a crime's location, a major step in the criminal justice path.
Evidence from the smallest biological samples - sweat on a collar, the cells on a toothbrush - is becoming increasingly important to the criminal justice system. DNA evidence can debunk a defendant's claims, help victims find closure and keep innocent people out of jail.
The state's attorney's office in Harford has used DNA evidence since about 1990, when a private lab did the work. DNA evidence can come from almost anywhere, said Cpl. Diane Newton, the supervisor of the evidence collection unit at the Harford County Sheriff's Office.
Newton's unit photographs and videotapes crime scenes, then collects the evidence, packaging about 1,200 pieces of biological and nonbiological evidence a year.
"When I first started in 1989, basically DNA [analysis] was not available, so it was much different," Newton said.
Although searching for potential DNA evidence has increased the unit's workload, the trade-off is well worth it, she says. "We're getting wonderful more relevance" from the evidence collected at crimes, she added.
Because the county's demand is too low to merit a DNA lab, law enforcement officials here send evidence, such as clothing, weapons and other leavings, to the Pikesville lab of the Maryland State Police. There, 17 people work in the biology unit, examining the traces of life that can help explain the past.
The state lab has profiled DNA since 1992, but only this year did it switch to a protocol that generated enough information to meet the standards of CODIS, the national database maintained by the FBI that can help investigators across the country match cold cases - those without suspects and often without other leads - to profiles from other crimes.
