Defense Disputes Forensic Blood Tests in Ex-Officer’s Murder Trial

Several small patches of dried blood and the esoteric techniques used to decipher the blood’s genetic secrets have become a hotly disputed issue in the high-profile murder case against former California Highway Patrol Officer Craig Peyer.

The prosecution hopes to use as evidence in Peyer’s upcoming trial blood stains found on a sweat shirt and boot worn by murder victim Cara Knott--stains that prosecutors say their analyses will show are unlikely to have come from anyone other than Peyer.

But Peyer’s defense lawyers have challenged the use of the tests, questioning whether they are reliable and scientifically accepted. They are asking the court to bar the prosecution from using some of the results in Peyer’s trial.

The dispute, which dominated pretrial proceedings in San Diego two weeks ago, appears to some experts to be another example of how lawyers are more likely to challenge scientific methods for drawing distinctions between samples of blood.

Called a Good Sign

Some lawyers say the challenges are a good sign--an indication of increasing awareness that the tests are not infallible. In the past, they suggest, lawyers and juries have been insufficiently skeptical of scientific evidence.

But some forensic scientists charge that the challenges are little more than a legal game. They say their techniques are both proven and, in many cases, commonplace. They say there is no question among scientists--just among lawyers--that the tests are valid.

“It’s sufficiently common that it’s certainly a cause of concern among the forensic science community,” John Thornton, a professor of forensic science at the University of California, Berkeley, said of recent efforts to exclude so-called serological evidence from court cases.

“The forensic science community is being jerked around somewhat by this attack,” Thornton added in a recent telephone interview. “This is a successful legal attack, but it’s not a scientific attack.”

In the Peyer case, the issue is rooted in several small blood stains found on the clothing of Miss Knott, the 20-year-old San Diego State University student Peyer is accused of having strangled and dumped off a bridge near Interstate 15 on Dec. 27. Peyer was fired May 29 after the CHP conducted an internal investigation.

After Peyer’s arrest, law enforcement officials took a fresh sample of his blood and had it “typed” by forensic scientists, a technique that entails conducting tests to identify distinctive characteristics in the blood known as “genetic markers.”

Since that time, the forensic scientists have begun comparing Peyer’s blood to the stains found on Miss Knott’s clothes. They have also compared the stains to a known sample of Miss Knott’s blood to determine whether the blood stains came from her.

In the case of the stain on Miss Knott’s boot, a criminologist testified during the pretrial hearing that it matched Peyer’s blood for all three markers for which he tested. Two of the three markers differed from the markers found in Miss Knott’s blood.

Different Test

Another lab has done a different test on the sweat shirt stain, looking for two additional markers. The results of that test, according to court papers, “excludes the victim as a possible donor but includes the defendant.”

The San Diego district attorney’s office intends to have tests for additional markers done on the stains, Assistant Dist. Atty. James Atkins said, adding that the office decided to “exhaust the stain and test for as many markers as possible.”

“The theory is that it’s her murderer’s blood on her,” Atkins said. “It’s a whodunit: Who’s blood is it? By testing as many markers as possible, we narrow the possibilities.”

The tests that Peyer’s lawyers are most aggressively contesting are tests for so-called Gamma and Kappa markers. Those markers are antigens in blood serum that come in many types. Atkins said the type of so-called Gm marker in Peyer’s blood is “very rare.”

The tests for those markers were developed in the 1960s and have been used widely in Europe since then, proponents say. But because certain reagents used in the tests were unavailable until recently, the tests have been used only since the mid-1980s in the United States.

Peyer’s lawyers have contended in court papers that the technique falls short of the standard for scientific evidence in California courts, which requires that any procedure be generally accepted by the scientific community before the results are admissible.

“We argued in our motion that it is our belief that there are approximately four forensic labs out of hundreds in the United States that use this type of testing,” said defense lawyer Robert Grimes. “We feel that that’s because it just isn’t accepted.”

Grimes and Diane Campbell, Peyer’s other lawyer, also initially challenged a second form of testing used to compare one stain to Peyer’s blood. However, they dropped that objection two weeks ago after testimony before Superior Court Judge Richard Huffman.

Distinctive Enzymes

That technique, used by the San Diego Police Department, entails testing for so-called ABO antigens and for certain distinctive enzymes in the blood. The enzymes involved in the Peyer case are Phosphoglucomutase (PGM) and Esterace D (EsD).

Those enzymes and many others are known to be “polymorphic.” That is, they come in numerous types that vary within populations. So over the last 15 to 20 years, the tests to identify them have played an increasing role in blood typing.

“They’re used every day across the country,” said Thornton, the forensic scientist at UC Berkeley.

Nevertheless, Thornton said last week that he had noticed an increasing number of challenges recently to admitting such evidence in court cases nationwide.

In some recent cases, in states including California, courts have acceded to requests to bar blood-typing evidence (though experts acknowledge that such evidence is still allowed in the vast majority of cases in which it has been used).

Randolph Jonakait, associate dean of New York Law School in Manhattan, traced the trend in part to a lengthy critique of blood typing that he wrote and had published in 1982 in the Emory Law Journal. (The article has been cited extensively in papers submitted by the defense in the Peyer case.)

In that article, Jonakait argued that new methods for identifying genetic markers had put “a tremendous new tool” in the prosecution’s hand. Yet, he said, there had been few objective, scientific studies to determine whether the tests were reliable.

He said the literature did contain “proven and potential areas of unreliability in the tests’ uses.” For that reason, he argued that the tests’ results should not be admitted in court until the techniques had been rigorously studied.