Prosecutors Begin Crucial DNA Phase of Simpson Case : Trial: Lab director gives a primer on the complex subject. She does not refer to tests involving defendant.

More than three months after promising jurors that DNA test results would connect O.J. Simpson to a pair of bloody homicides, prosecutors began the task Monday of presenting that crucial evidence, opening the most important phase of their case with a brief seminar on genetics.

Robin Cotton, director of the nation’s largest private DNA laboratory, began her testimony by delivering a primer on how DNA works, peppering her lecture with a series of metaphors intended to illuminate the scientifically dense topic. At various points, Cotton compared DNA to an alphabet, a thread, a zipper, a pair of interwoven ribbons, a chapter in the genetic book that is the chromosome, and a blueprint for human development similar to the plans for erecting a building.

“If we make the assumption that a blueprint contains all the information for how to build your house,” she said, “the analogy is that DNA contains all the information on how to build you.”

Though she did not describe any results of DNA tests performed by her laboratory in this case, prosecutors say those results will reveal a trail of blood linking Simpson to the murder scene--showing that blood with some of his genetic characteristics was at the scene and that blood apparently from both victims, Ronald Lyle Goldman and Nicole Brown Simpson, was found inside his car and at his Brentwood estate.

Simpson has pleaded not guilty to those killings, and his legal team is prepared to mount an aggressive challenge to the DNA evidence.

Looking directly at jurors and speaking in a soft, clear voice, Cotton illustrated her testimony Monday with neatly drawn charts on sheets of butcher’s paper. She told jurors that degradation of DNA samples never would cause a sample to falsely point to a suspect, a notion that defense attorneys have hinted at for weeks.

Testifying on a day cut short by the funeral of a revered Los Angeles police detective, which Superior Court Judge Lance A. Ito and other trial participants wanted to attend, Cotton was guided through her testimony by Deputy Dist. Atty. George Clarke, one of the most experienced DNA prosecutors in California and the fourth government lawyer to examine a witness in the Simpson case.

The combination of a knowledgeable witness and an experienced lawyer made things go smoothly for the prosecution. Cotton fielded questions easily and moved briskly through the array of topics. And both lawyer and witness paid special attention to detail: When Cotton finished one of her charts, Clarke pointed out that she had neglected to cross the letter “t” in one place. She nodded, added a line and moved on.

It has been months since the easygoing Clarke, whose friends call him “Woody,” was first introduced to the jury. With the judge’s permission, he opened his examination Monday by reacquainting himself with the panelists. Clarke told jurors that his name ends with an “e” and thus assured the panelists that he is not related to lead prosecutor Marcia Clark.

“I didn’t need that disclaimer, your honor,” Clark said jokingly, drawing chuckles from the judge and audience.

Lively Science

Although many trial watchers have braced for at least a month of dull, scientific testimony on DNA, Cotton’s initial appearance was delivered brightly and illustrated simply. Under questioning from Clarke, who consulted typewritten notes in a loose-leaf binder, Cotton wove her observations about the basic science of DNA with her qualifications and with the history of her company, Cellmark Diagnostics in Germantown, Md.

Many of the jurors took copious notes--a few have filled multiple notebooks since the beginning of the trial--and most seemed attentive during Monday’s session. Even when some of the attorneys seemed distracted, jurors paid close attention, turning back and forth between the attorney and the scientist.

Cotton, an experienced witness who said she has testified in about 90 cases, held that attention with an approach similar to that of a high school biology teacher. She meticulously addressed each of her points, starting with basic definitions of terms such as molecular biology, biochemistry and DNA, and building toward the specific techniques employed by Cellmark, one of several laboratories that have tested samples in the Simpson case.

Cotton told jurors that DNA is present in nearly all human cells--with the major exception of red blood cells--and reminded the panelists that all people get their DNA from their parents. Although more than 90% of a person’s DNA is common to all people--a common stock that reflects the similarities of all humans--the balance is highly individual, she said.

“That’s intuitively obvious because you can look around even in a very large room . . . and you’ll see that with the exception of identical twins, people are different,” Cotton said. “Even closely related people, brothers, two brothers, are different. You can always tell them apart. And the exception is identical twins. And identical twins are identical because they have identical DNA, and that is the only exception.”

Scientific concepts such as that are important building blocks in the prosecution case because within a day or two, prosecutors expect to begin introducing DNA test results showing that blood found at the crime scene contained genetic markers matching those found in a sample of O.J. Simpson’s blood. The odds of those two samples coming from different people are extremely small, a notion that is based on the highly individual nature of DNA.

Throughout her testimony, Cotton attempted to present simple analogies for complex testing procedures and ideas. Explaining how the results of a particular kind of DNA testing are transferred from a gel to a nylon membrane used to preserve the results, for instance, Cotton laid out a sample of the nylon on the edge of the jury box and described the technique as a simple one that made use of paper towels.

The towels, she said, soak up the liquid surrounding the strands of DNA much like a person wipes up a stain. The DNA is trapped in the nylon membrane, where it can be tested and photographed. That process, she added, is so strikingly simple, “you could set it up in your kitchen, if you really wanted to.”

“It’s not a very elegant contraption,” she added. “But this is one of the most important procedures in all of molecular biology, and it’s used all over the world.”

DNA: History, Application

Given the chance to provide a brief history of DNA testing, Cotton cited various important breakthroughs and emphasized the important role played by a British scientist who worked with Cellmark in establishing the company. That scientist, Clarke noted, was knighted for his work.

Some of the basics of DNA research were discovered in the 1950s--Cotton recalled for jurors a breakthrough article in 1953--while other developments in recent decades have cleared the way for greater forensic application of the procedure. Clarke guided Cotton through that history, and she noted that each of the scientists had built upon the work of others, emphasizing for the jury the enormous body of distinguished research that has contributed to the science now being applied in the closely watched murder case.

Moreover, Cotton diverged from the Simpson case to list DNA testing’s many applications outside the criminal-investigation process. Similar techniques, she said, are being used to identify war dead, to diagnose and prevent certain diseases, to pinpoint the fathers of children in paternity cases and even to find poachers who have killed endangered species by sampling meat from their freezers and determining what kind of animals it came from.

That broad description of the usefulness of DNA testing may strengthen its credibility when prosecutors present the results of tests implicating Simpson, some legal analysts said.

“Cotton made reference to criminal investigations a very low percentage of the time,” said Karen Smith, a Southwestern University law professor. “She described DNA testing in a way that is completely neutral, not just a tool of the prosecution. I think that’s going to pay off. Having set it up in this neutral fashion, the prosecution plans to use DNA as its strongest weapon to point the finger at O.J. Simpson.”

Paul Mones, a Santa Monica defense lawyer and author of the forthcoming book “Stalking Justice”--about the first homicide case in the nation in which a man was convicted of murder solely on the basis of DNA evidence--agreed.

“The notion is if you can use DNA on the battlefield, if you can use it to identify paternity, to identify genetic diseases, then of course it’s reliable technology to be used in a criminal justice setting,” he said, adding that Monday’s biology lesson was typical of the way prosecutors generally begin introducing juries to the topic of DNA evidence.

“This,” he said, “is the classic way that DNA is introduced in trials throughout the United States.”

Near the end of her testimony, Cotton gave jurors a preview of what is to come, as she testified that her lab had indeed gotten results from DNA analysis known as RFLP tests--one of two major types of DNA testing. Clarke also posed a series of questions to her that were intended to discredit the defense suggestion that degraded blood samples might have produced false results in some tests.

“If DNA suffers this . . . degradation process, will that result in changing of the types from the original type of the sample to a new and different type?” Clarke asked.

“No,” she responded. “It will not.”

“So this process of degradation, can it change my DNA into looking like your DNA?” the lawyer continued, emphasizing his point.

“No,” Cotton said.

“Or your DNA into looking like the court’s DNA?” Clarke asked, nodding in the direction of Ito.

“No,” she said again.

Truck Driver Testifies

Cotton, who will return to the witness stand today, was called after a brief appearance by tow-truck driver Bernie Douroux, who testified about towing Simpson’s Ford Bronco from his Rockingham Avenue estate on the day after the killings.

Douroux spent less than 30 minutes on the stand, a record for speedy testimony in a case where some relatively minor witnesses have been subjected to extraordinarily probing questioning.

Although neither side made much of Douroux’s account, prosecutors called him to establish the chain of custody for the car--which witnesses already have said was found stained with blood--and Simpson attorney Johnnie L. Cochran Jr. used his brief questioning to raise still more doubts about the police handling of evidence.

Douroux testified that he never had unlocked Simpson’s car or touched the door handle and that he had left it inside a locked LAPD print shack after driving it across town from Simpson’s house on the day after the murders. Under cross-examination, Douroux acknowledged that he had briefly left Simpson’s Ford Bronco unattended outside police headquarters that afternoon and also said he had not noticed blood inside or outside the car when he picked it up or dropped it off.