Testifying Friday in the murder trial of O.J. Simpson, a leading statistician conceded that he had botched a set of calculations related to DNA tests in the case--an admission that had little direct bearing on the evidence but that defense attorneys used in an effort to undermine his credibility.
Bruce Weir, a nationally recognized professor of statistics at North Carolina State University, spent the morning filling in a few remaining details in the prosecution's DNA evidence charts, in a session that jurors followed with mild interest.
But the panel snapped to attention as Weir, whose New Zealand accent and impressive academic credentials convey an air of authority, was challenged for mistaken calculations by defense lawyer Peter Neufeld. The attorney confronted Weir with his own charts, noting that Weir had calculated some DNA frequencies by assuming that a particular genetic marker was present while at the same time omitting that marker from other calculations.
"If I did not include them, I am sincerely sorry," said Weir after reviewing the material. "I am also embarrassed."
Two of the jurors looked at each other with raised eyebrows when Weir said that. Virtually all the panelists seemed to take note, scribbling in their pads as Weir testified.
The DNA evidence forms the core of the prosecution case against Simpson, who has pleaded not guilty to the murders of Nicole Brown Simpson and Ronald Lyle Goldman. Although some other aspects of the prosecution case have been marred by slip-ups, the DNA evidence has unfolded smoothly for the most part.
In fact, Weir's direct examination by the prosecution ended strongly, with the analyst vouching not only for his own results but for those produced by the two laboratories that performed the DNA analysis in the Simpson case.
As a result, Friday's admission by Weir came as a surprise and was trumpeted by the defense, even though the statistics that it affects only involve a few of the less significant DNA samples in the case. Outside court, prosecutors acknowledged that when the figures are recalculated, they will be slightly less significant, but they downplayed the effects of Weir's miscalculations.
"It's going to have a minimal effect," said Deputy Dist. Atty. Lisa Kahn, a leader of the prosecution's DNA team.
In the context of the overwhelming bulk of DNA evidence in the case, Weir's miscalculation of a few results amounts to "no more than a speck of sand," Kahn said, adding that the scientist's willingness to acknowledge his error would only enhance his credibility with the jury.
But Neufeld suggested that the figures in Weir's reports might reflect more than errors, noting that in each of five tests in which the statistician failed to calculate the particular genetic marker, his erroneous findings tended to overstate the significance of evidence against Simpson.
"By failing to include the additional pairings . . . the numbers that are arrived at by you and put on that board are biased against Mr. Simpson, isn't that correct?" Neufeld asked.
"As it turns out," Weir said, "it looks that way, yes."
Nevertheless, Weir angrily rejected the suggestion that he was tilting his results to favor the prosecution.
"When I do calculations, I do not consider any forensic implications," he said, staring intently at Neufeld. "And if you are suggesting that I do, let me disabuse you of that right now."
Despite Weir's response and evident anger, Neufeld continued to hammer away at the theme, eliciting the statistician's acknowledgment that he never consults with or testifies on behalf of defendants, only prosecutors. Weir had testified earlier that he did not work for defendants because he strongly believes in the forensic applications of DNA evidence, but Neufeld attempted to suggest that his beliefs amounted to bias.
The confrontation between the defense attorney and the scientist was a charged one--the two men know each other professionally, but until Friday had never faced each other across a courtroom--and they sparred in front of the jury as well as outside its presence.
Before the jury was brought into the courtroom, Neufeld asked for copies of data underlying some of Weir's charts. Weir, who said he had been up until midnight the night before working on the calculations, primly refused to work Saturday in order to comply with the defense request.
"I'm not going to work Saturday," said Weir. "I'm quite tired."
"As we all are," added Ito. "We're all glad it's Friday."
Another Lawyer Fined
During the cross-examination, tempers rose again, particularly when Neufeld attempted to question Weir about a letter that a group of scientists wrote to Nature magazine. Ito had previously warned the defense about using that letter, and when Neufeld touched on it Friday, prosecutors objected and the judge quickly intervened.