Simpson’s Team to Push DNA Data as ‘Irrelevant’ : Trial: Defense lawyers say if evidence was contaminated or tampered with, the numbers are meaningless. They concede that the statistics presented by the prosecution were staggering.

Confronted with numbers that dizzyingly suggest O.J. Simpson’s guilt, his lawyers have constructed a two-tiered defense: Chip away at the statistics by suggesting laboratory error and then attempt to undermine the numbers completely by claiming that the evidence they reflect was contaminated by police.

“The defense position is really: If there is cross-contamination or tampering, all those numbers are irrelevant,” Peter Neufeld, one of Simpson’s nationally renowned DNA attorneys, said in an interview. “Even if you had sent these samples to three labs or to four labs or to 100 labs, it makes no difference.”

Persuading jurors that the numbers are meaningless--or at least that they lack the wallop that prosecutors assert--is an essential task for the Simpson lawyers as they labor to show that their client is not guilty of the murders of his ex-wife Nicole Brown Simpson and her friend Ronald Lyle Goldman.

In dramatic fashion last week, prosecutors unveiled the first round of their DNA evidence. The statistics, presented by Robin Cotton, director of the Maryland-based Cellmark Diagnostics DNA laboratory, were staggering, even by the defense’s admission.

According to Cotton, blood near the victims could only have come from one in 170 million people--yet it matched Simpson’s; blood on a sock in Simpson’s bedroom only is consistent with one out of at least 6.8 billion people--yet it matched that of his murdered ex-wife.

“If you accept the science, and it’s hard not to accept the science, the prosecution’s case now looks overwhelming,” said Los Angeles criminal defense lawyer Harland W. Braun.

Deputy Dist. Atty. Rockne Harmon, one of the Simpson prosecution’s DNA specialists, assertively echoed that opinion in court Friday after the jury had left. Describing the DNA evidence as a “mountain,” Harmon said it had “begun to cascade right where it belongs--on Mr. Simpson.”

But litigating DNA is the longtime specialty of Neufeld and his partner, New York attorney Barry Scheck. And the unfolding drama in the Simpson case is merely the latest round in a fierce legal debate over DNA and its application in the criminal justice system.

“This is like two chess grand masters with a long history of combat,” said UCLA law professor John S. Wiley Jr. “Every new battle follows months of study.”

As the defense launches its counterattack, Simpson’s lawyers are employing a strategy that is as simple as it is subtle.

First, they hope to persuade the jury that the statistical data used to produce those astronomical numbers is flawed and contested by leading experts. They bolster that position with a list of eminent scientists, 26 of whom wrote to Nature magazine in November to stress that the statistical significance of “matches” can never be better than a lab’s error rate.

The issue, they say, is that the statistical significance of a match is reported as the likelihood that a sample came from anyone other than a particular person. When Cotton or the Simpson prosecutors say that the likelihood is 1 in 6.8 billion or more, they mean that those are the odds against another person having the same genetic characteristics.

But what about the odds that the laboratory made a mistake and falsely implicated a person? Or the odds that evidence was contaminated or planted?

“If the probability of a random match . . . is one in 50 million, but laboratory error creates false positives one time in a 100, then the true rate of erroneous match is . . . about one in a 100,” the scientists wrote in their letter, which was never published but which was obtained by The Times.

It is believed that the letter was not published because the magazine has a policy of not running letters signed by more than one person.

Jerry A. Coyne, a professor in the University of Chicago’s department of ecology and evolution and one of the authors of that letter, said Saturday that the Simpson prosecution has ignored the concerns that he and his colleagues raised in their letter.

“When Robin Cotton says ‘one in 6 billion,’ she assumes that if Cellmark conducted 6 billion tests, Cellmark would make just one error,” Coyne said, who has worked as a consultant to the Simpson defense team. “I just don’t believe that.”

In fact, Coyne and others say Cellmark has only submitted to so-called “blind testing” of its laboratory twice, and both times it falsely identified one sample out of about 50. To critics of the lab, that suggests an error rate of 2%.

In recent years, Cellmark has not undergone blind testing--a process in which a lab is sent samples but not told that they already have been identified and that the only real purpose is to test the lab’s proficiency. Because Cellmark has not submitted to such tests, Coyne and Neufeld said it is impossible to know the laboratory’s error rate.

“When someone floats a number like that, whether it’s 170 million or 6.8 billion, one of the questions that is raised is the same as in anything that involves humans: What is the rate of error?” Neufeld said.

Other factors can influence the statistical meaningfulness of a match, according to Coyne and others. There are questions about the accuracy of the databases upon which the numbers are based, as well as on the way the process classifies different racial groups. One of the databases used by Cellmark relies upon a study of blood samples from fewer than 300 African Americans living in Detroit. Because that sample is so small, it raises doubts about the validity of the study, some experts say.

Santa Monica defense lawyer Brian C. Lysaght, a former federal prosecutor, said there is “a lot of voodoo mathematics with DNA, particularly when it comes to the the size of the sample on which these definitive conclusions are based.”

Although the statistical arguments can be densely scientific and statistical, they dovetail with the defense’s central response to the DNA evidence: the contention that the blood samples submitted to Cellmark and a state Department of Justice lab were contaminated before they left the LAPD.

No matter what Cellmark’s error rate is, Neufeld and his defense colleagues say it is bound to be better than that of the LAPD. Neufeld attempted to illustrate that point during his initial cross-examination of Cotton last week, confronting her with a series of questions about the Police Department’s handling of samples.

Superior Court Judge Lance A. Ito cut short that inquiry because Cotton testified that she did not have direct knowledge of the Police Department’s procedures, but the defense has argued throughout the case that contamination or tampering with samples could have occurred while they were in the possession of the LAPD.

By contrast, assistant LAPD crime lab director Gregory Matheson defended the work that he and others in the lab did, acknowledging that some aspects of the evidence collection could have been better but repeatedly and confidently testifying that the police had done nothing that compromised the evidence.

Still, the defense has suggested that, at best, the blood samples taken from the scene of the crimes and Simpson’s home and Bronco were carelessly stored and improperly handled. At worst, they argue that evidence was intentionally tampered with by police eager to frame Simpson for the murders. They have offered no direct evidence of any such conspiracy.

In the interview with The Times, Neufeld said the defense will return to those themes in order to draw the contrast between Cellmark’s performance and that of the police. The implication, Neufeld said, is that if Cellmark has produced false results, the LAPD is bound to be even worse--a contention based partly on the LAPD lab’s lack of accreditation.

“If a lab that considers itself the best in the business has made false positives in proficiency tests,” he asked, “what can we say about one of the worst?”

Other observers have their doubts about how successful the defense will be in making those points, particularly when it comes to accusing the police of intentionally fabricating evidence.

“Frankly, if you look at the LAPD’s history, it’s clear that a conspiracy this elaborate is beyond their competence,” said Braun, who won an acquittal for one of the Los Angeles police officers accused of violating Rodney G. King’s civil rights. “It’s just inconceivable that they could have concocted a scheme this elaborate and sophisticated in so short a time.”

In defense of their approach, Simpson’s lawyers have long stressed that they are speaking to the jury, not to the pundits. And in a city where suspicion of the Police Department runs high in some quarters, the challenge to the DNA evidence is merely one part of the Simpson team’s attack on the police.

Still, say some observers, even if the defense can succeed in whittling away jurors’ confidence in the DNA statistics, that may not be enough to carry the day for the accused former football star.

“Even if there are more than one in 170 million people with this DNA, how many of them were married to this woman, had beaten this woman, had access to her condominium, had a possible motive and had drips of blood on their own premises?” asked Georgetown law professor Paul F. Rothstein. “It’s still powerful evidence pointing to O.J. Simpson.”