The same DNA test Anne Arundel prosecutors used last week to help convict Scotland E. Williams of the murders of two Washington lawyers is being used more frequently by prosecutors in the country to boost their chances of getting a conviction.
Use of the polymerase chain reaction (PCR) test is increasing "exponentially," said Clay Strange, the director of the Legal DNA Unit at the American Prosecutors Research Institute in Northern Virginia.
No one has kept an exact count of the number of times PCR evidence has been used since its introduction in criminal trials in the late 1980s. But chemists at the largest private DNA testing lab in the country used the test in about half the 2,000 criminal case samples they received last year, compared to less than 10 percent in 1993, said Mark D. Stolorow, manager of Cellmark Diagnostics in Germantown.
Cellmark is the lab that tested the DNA evidence for the O. J. Simpson murder trial in Los Angeles.
The Maryland State Police Lab only last week began doing the test and already has 12 samples from police agencies in the state, director Dr. Louis Portis said.
"It's frequently admitted as evidence because courts are very reluctant to pass up a technique when the prosecution strongly advocates it," said Walter Krstulja, the forensic science coordinator at the Los Angeles Public Defender's Office.
PCR-DNA was first used in a Maryland courtroom in April 1993 in the trial of Albert G. Givens, a handyman convicted of murdering and sexually assaulting a woman in her Arnold home. A key piece of evidence was a microscopic speck of saliva taken from a soft drink bottle at the scene and linked to Givens through the PCR test. He was sentenced to life in prison.
PCR evidence is to be used in the case against Darris Ware, who is charged with killing two women in Severn. That trial is scheduled to begin in September.
Mr. Strange, who was a state's attorney for nine years in suburban Dallas, said the Williams trial is an "excellent" example of how the test, combined with other evidence, can be used to place the defendant inside a victim's home. Williams, who could receive the death penalty, has a sentencing hearing tomorrow.
"[The PCR test] was one piece of evidence," said State's Attorney Frank R. Weathersbee, who will argue that Williams should be sentenced to death for killing Jose Trias, 49, and his wife, Julie N. Gilbert, 48. "I don't think you would be able to convict someone with that alone."
Mr. Strange agreed.
"It is another piece of evidence that the courts have agreed helps a jury make their decision of guilt or innocence," he said.
Maryland appellate courts have yet to rule on the use of PCR tests. The tests have been allowed in 12 of the 13 criminal cases reviewed by appellate courts in other states, according to court records. Trial judges in 36 states have allowed the test to be used as evidence.
The more common restriction fragment length polymorphism test is admissible in court under state statues. But the PCR test only can be admitted by a judge.
While the PCR test is useful to prosecutors during trials, it also helps them eliminate suspects during an investigation, Mr. Strange said. For example, police in Ellis County, Texas, arrested a 30-year-old unemployed drifter for allegedly kidnapping and sexually assaulting an 88-year-old woman. Police sent a semen sample from her clothing to a lab for PCR testing, Mr. Strange said.
"He matched the description the woman gave us, he was seen near the grocery store where she was kidnapped just before the crime, and he had been charged but never convicted of sexual assault before," he said. "So the circumstantial evidence was strong. But sure enough, the test came back without a match."
The charges were dropped, and the man was released. The case remains unsolved, Mr. Strange said.
The technique also is useful to police and prosecutors when a homicide victim's body has been exposed to the elements, causing tissue samples to degrade, said Mr. Strange, who used the test to convict a 19-year-old man of murdering two teen-agers three years ago.
"One of the reasons we had to use PCR in that case was that the bodies were exposed to the summer Texas heat and the samples had degraded," he said.
While PCR has been embraced by some defense attorneys whose clients it has cleared, others argue against using it when it is part of the state's evidence.
The test's critics say that because the procedure amplifies a tiny sample of body fluid, the risk of contamination is high.
"It's like glorified blood testing," said Robert Waldman, an Anne Arundel County public defender. "You have to make sure you are boosting what you want to boost and not another fluid that has gotten into the sample."
Mr. Waldman and other defense attorneys say PCR is reliable when it is used to exclude a suspect, but it is not the "fingerprint" that positively identifies someone as prosecutors like to claim. In the Williams case, the test showed that 889 lTC others in the black population had the same type of DNA that was scraped from a glass found in the kitchen of the victims' home.
Defense attorneys also say that some labs, such as Cellmark, are regulated by the American Association of Crime Labs, but not by a government agency and do not have to make their error rates public.
"It's ridiculous because you even need regulations to get a cholesterol test," Mr. Krstulja said. "Without quality controls, the test should not be used to help convict."
Defense attorneys also worry that a jury could convict an innocent person based on the prosecution's word that the test is infallible.
"There is magic to the word DNA," Mr. Waldman said. "But a jury has to be sophisticated enough to sort through it."