Updated June 5, 2004, 12:28 p.m. ET

O.J. Simpson: Week-by-week

Week 16

May 8 - 12, 1995

MAY 8 - Court became biology class Monday as the prosecution's first DNA expert lectured to the jury on her specialty.

Dr. Robin Cotton, laboratory director of Cellmark Diagnostics Inc. in Germantown, Maryland, described DNA as a genetic blueprint. The DNA in each person is different, with the exception of identical twins, she said.

The testimony is a prelude to DNA evidence that prosecutors will use to try to tie O.J. Simpson to the June 12 murders of his ex-wife and her friend Ronald Goldman.

Cotton, a molecular biologist and the 44th witness in the trial, explained the process known as RFLP, or Restriction Fragment Link Polymorphism, which she said is the most accurate method to test DNA. Cellmark is the largest independent DNA testing laboratory in the United States.

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To undermine the defense claim that sloppy police work ruined the integrity of key evidence, Prosecutor Woody Clark asked if the degradation of a blood sample can make the DNA look like that of another person. Cotton said no.

Cotton has testified in about 90 cases in more than 20 states. She used colorful charts to illustrate her points.

Court recessed at 1 p.m. because Judge Lance Ito planned to attend the funeral of a police detective who died last week. The direct examination of Cotton will continue Tuesday.

Prosecutor Clark was making his first appearance in the trial. He is a DNA legal expert on loan to the Los Angeles District Attorney's Office from the San Diego District Attorney's Office.

Earlier in the day, tow truck driver Bernie Douroux testified that he towed Simpson's Bronco from Simpson's home to the LAPD garage. Prosecutors wanted to show he found the car locked to discredit the defense claim that evidence was planted in the vehicle.

MAY 9 - In the final minutes of testimony Tuesday, jurors saw DNA samples of O.J. Simpson and the two murder victims for the first time.

With no eyewitness testimony, the prosecution case largely rests on the strength of DNA evidence placing Simpson at the murder scene, which will be shown to the jury in the coming days.

Jurors saw copies of x-ray pictures of DNA fragments, known as autorads, from Simpson, Nicole Brown Simpson and Ronald Goldman. The autorads were made from blood samples taken after the June 12 double murder.

In upcoming court sessions, these autorads will be compared with those from blood collected at the murder scene, Simpson's home and his car.

Lawyers spent much of the day battling over how evidence that contains more than one person's blood, known as mixed-blood evidence, should be presented to the jury.

Outside the presence of the jury, the defense argued that the prosecution should have to prove the accuracy of mixed-blood tests. The prosecution wants to present test results and let the jury decide on the credibility of the tests.

Speaking to reporters outside the courtroom, Prosecutor Rockne Harmon said some of the blood left on the glove found in the back yard at Simpson's estate matched that of Goldman and the football star's ex-wife.

Prosecutors also said a stain found on the steering wheel of Simpson's white Ford Bronco contains a mixture of DNA from Simpson and someone who may not be connected to the case. The mixture is inconsistent with the DNA of the two murder victims. It could have come from anyone who drove Simpson's car, they said.

Testimony on DNA tests performed on blood samples taken at the crime scene is expected to come from Dr. Robin Cotton, laboratory director at Cellmark Diagnostics Inc., which performed most of the DNA tests on blood found in the investigation.

Cotton described for the court the difference between the two primary genetic fingerprint tests in testimony Tuesday. She said the so-called RFLP test was more reliable than the other DNA test, known as PCR.

The advantages of PCR tests are that they take less time to perform and require a smaller blood sample, she said. PCR testing was required for much of the evidence in this case because samples were too small to conduct the other test.

MAY 10 - In the first testimony that directly linked O.J. Simpson to the murder scene, a forensic scientist testified that DNA tests showed a genetic match between Simpson's blood and stains found near the bodies of his former wife and her friend.

Dr. Robin Cotton, the laboratory director of Cellmark Diagnostics in Germantown, Md., also said the tests showed that small blood stains on a sock in Simpson's bedroom had the same genetic blueprints as Nicole Brown Simpson.

The defense is expected to argue that the incriminating evidence against Simpson was tampered with by police before it was sent to the scientists for testing.

The prosecution has argued that Simpson cut his hand while slashing the victims, leaving blood drops at the crime scene and his home. Since there are no eyewitnesses and police never found a murder weapon, the heart of the state's case rests with the DNA tests of the blood evidence.

Testifying in a soft-spoken, calm manner, Cotton focused on three pieces of evidence: a blood drop from the foyer of Simpson's Rockingham home; a blood drop from the Bundy crime scene and a blood drop found on Ronald Goldman's shoe.

She said the blood drop lifted from Simpson's foyer contained DNA with the same distinctive series of genetic markers as Simpson's blood.

A sock found at the foot of Simpson's bed tested positive for blood, and Cellmark's analysis of DNA extracted from the sock showed that the blood could have come from Nicole Simpson. O.J. Simpson and Goldman were excluded as possible DNA "donors."

Though blood on the bottom of Goldman's shoe was difficult to analyze, Cotton testified that several genetic markers were consistent with Nicole Simpson's blood.

MAY 11 - The prosecution introduced DNA test results to show that it was virtually impossible for anyone other than O.J. Simpson to have left a bloody trail at the murder scene and at Simpson's home.

Robin Cotton, laboratory director of Cellmark Diagnostics in Germantown, Md., testified that the deoxyribonucleic acid (or DNA) banding pattern found in a sample of Simpson's blood, in a blood spot on the Bundy Drive crime scene walkway and in blood from the foyer of Simpson's Rockingham home was extremely rare.

In the most powerful evidence yet presented against Simpson, Cotton testified the odds that blood found at the scene of his wife's murder could have come from anyone but Simpson were about one in 170 million.

Cotton said that blood found on one of Simpson's socks and identified as Nicole Brown Simpson's blood, had DNA characteristics matched by approximately only one in 9.7 billion Caucasians, meaning she was the only person in the world with that match.

The numbers, Cotton testified, were based on statistics extrapolated from a database of various DNA types kept at the Cellmark lab. They indicate the chances that someone would randomly match a certain DNA profile, Cotton said.

Defense attorney Peter Neufeld started his cross-examination of Cotton by suggesting that some blood from Simpson's home may in fact be Simpson's, while blood at the crime scene may have been contaminated or tampered with.

Neufeld also challenged Cellmark's statistical calculations on the grounds that its database relied only on DNA taken from several hundred people in Detroit. The lab's database of African-Americans was obtained from the Detroit Red Cross and consists of 240 African-Americans. Neufeld wanted to know how Cotton could get numbers in the billions from such a database.

The statistics are calculated by multiplying the frequency with which genetically independent markers appear in an individual's DNA, which is found in every cell in the body.

Cotton explained that in addition to the Restriction Fragment Length Polymorphism (RFLP) test results, another DNA test called Polymerase Chain Reaction (PCR) analysis showed that Simpson's DNA banding pattern appeared to match DNA from a blood drop near the victims' bodies, a drop from the Bundy Drive walkway leading to the rear of the residence, as well as a blood drop from driveway of Simpson's home.

And PCR tests also indicated that the nail scrapings and clippings from Nicole Simpson's body appeared to be her own.

Defense attorneys have contended, since the start of the case, that the blood found under Nicole Simpson's fingernails contains blood from an unknown assailant.

MAY 12 - The defense continued its cross-examination of a forensic scientist who offered powerful testimony linking O.J. Simpson to the murders of his former wife and her friend.

Defense lawyer Peter Neufeld tried to undermine the evidence on several grounds in order to bolster the defense claim that the statistics overstate the significance of the "matches" and that the samples tested were tainted.

Neufeld continued to ask Dr. Robin Cotton, the laboratory director of Cellmark Diagnostics, if she knew whether certain scientists who disagree with DNA statistics are not accepted within the scientific community.

During the day, Neufeld tried to get Cotton to testify that police criminalists improperly collected the evidence, thereby tainting the DNA evidence. Neufeld apparently wanted to get across the idea that moisture and heat had degraded the DNA in such a way as to give wrong readings. But because Cellmark only tested the evidence after someone else collected it, Judge Lance Ito did not give Neufeld much leeway in questioning Cotton about the collection procedures. Cotton did admit that putting bloodstains in plastic bags and leaving swatches in a locked truck without air conditioning would not be her first choice of procedure. She also suggested that real harm would only be caused if the evidence was treated this way for an extended period of time.

Neufeld also raised the possibility that a bloodstain on the steering wheel of Simpson's Ford Bronco may have been left by a mystery killer. According to Cotton, the blood was a mixture of two people's DNA. Simpson and his former wife were a possible source, but one genetic marker in the blood was from an unknown source. Neufeld used this opportunity to raise the conspiracy angle by asking Cotton whether someone could have touched Simpson's blood, touched Nicole Simpson's blood and then touched the steering wheel. Judge Ito sustained a prosecution objection to the question.


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