DNA evidence focus of rape trial
By EARL KELLY
Journal staff writer
Trial continued yesterday of a Tobytown man charged with raping a Potomac woman in 1997, but the use of DNA in criminal prosecutions may be on trial as much as the defendant.
Paula Yates, a forensic supervisor at Cellmark Diagnostics Inc. in Germantown, spent most of the day answering defense attorney Leonard R. Stamm's questions about the adequacy of DNA testing that led to the arrest and indictment of Raymond Davis Wilson.
Half a person's DNA comes from his father and half from his mother, Yates said, a point Stamm considered significant because witnesses testified earlier that police initially considered a brother of Wilson a suspect in the rape.
"If a relative of a suspect is also a suspect, then his DNA should be examined, shouldn't it?" Stamm said, noting that DNA testing cannot distinguish between brothers.
Yates disagreed, saying in "many cases" DNA
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testing can distinguish between brothers.
"DNA is the genetic material of all living things," Yates told Assistant State's Attorney Debra Dwyer. All humans are 99.9 percent the same, with only one tenth of 1 percent of the DNA differing between people.
Preliminary testing showed that "only one in 14,000 African-American people would have the same DNA markers" as Wilson, Yates said.
"He cannot be excluded as the source" of the DNA collected from the rape victim, Yates told jurors when questioned by Dwyer.
But on cross-examination Stamm demanded more detail about DNA.
"A DNA match is not the same thing as a fingerprint, is it?" he asked, indicating that fingerprinting can be used to positively identify a particular person, but DNA cannot. Yates said, "Correct."
Stamm's argument was that DNA testing can be used to exclude someone as a suspect but cannot be used to positively identify an assailant.
Prosecutors say Wilson, 38, entered a one-story home on Pennyfield Lock Road by going through an attic window soon after midnight Dec. 17, 1997; Wilson then lowered the attic fold-down steps, entered the living area and raped the 73-year-old woman, they believe.
The assailant wore a ski mask, and the victim could not identify him. She said he did not wear gloves, but Wilson's fingerprints never were found at the house or on an envelope that prosecutors said contained money he stole.
After raising questions about DNA's reliability in identifying a particular suspect, Stamm focused on Cellmark's testing techniques.
Cellmark, in the preliminary testing that led to Wilson's arrest, looked at six regions of DNA.
Prosecutors have said Wilson was the one person in 50 million who could have raped the victim, but Stamm claimed outside of court that Cellmark later looked at three additional DNA regions, for a total on nine regions, to reach that conclusion.
Even with examination of the additional regions of DNA, Stamm says the testing was inadequate.
"The FBI requires 13 regions before it considers an identification as statistically reliable," Stamm said.
Besides trying to establish that Cellmark based its conclusion on too little evidence, Stamm attacked Cellmark's procedures.
Stamm asked Yates if contamination by different sources of DNA compromised the integrity of DNA testing, and she said it could.
He then asked her how many DNA samples a Cellmark technician works with at any one time.
"We all work several samples at the same time, we work with the number we feel comfortable with," she said.
Upon further questioning, Yates said she has worked with as many as 13 samples at one time.
Theodore Kessis of ADR Applied Resources of Columbus, Ohio, will testify later in the trial for the defense as a DNA expert.
"It's a tradeoff of methodology vs. costs," Kessis said outside the courtroom of Cellmark's running multiple samples at the same time.
Stamm attacked other aspects of Cellmark's testing including the fact that Cellmark relies on a small genetic base of about 100 blacks to compute its statistical sample.
The victim testified Monday she fought her assailant, scratched his face and hands, and bit his penis as hard as she could.
Police officers have testified they saw Wilson about 10 days after the attack, and he had a small scratch on his face and some small "nicks" on his hand, but his penis did not show signs of trauma.
Tammy Mindick-Mote testified for the prosecution yesterday that Wilson came to her home in Potomac a few hours after the events in question. He had some scratches on his face, but he said he got them running through the woods.
Wilson worked with Mindick-Mote's former boyfriend doing small construction jobs and gutter work, she said.
She said Wilson had a roll of money, and described it as a "wad" with $20 bills in it.
Prosecutors say the rapist in this case stole four $100 bills from the victim, and a witness said Wilson paid a cab driver with a $100 bill shortly after the rape was reported.
DNA evidence in this case caused prosecutors to reopen a 1991 Gaithersburg rape. They suspected Wilson in that case but did not have enough evidence to prosecute. A grand jury recently indicted him for the 1991 rape.