Defense in Belmont Shore Rape Trial Challenges Reliability of DNA Testing

The defense for Mark Wayne Rathbun, charged with sexually assaulting 14 women in their homes during a five-year string of attacks mostly in Long Beach’s Belmont Shore, wrapped its case Tuesday with testimony about error rates at three labs where his DNA was tested.

Laurence Dochez Mueller, a professor specializing in population genetics at UC Irvine’s department of ecology and evolutionary biology, said he found flaws in some testing protocols at two of the labs and projected likely error rates for all three, although he said none of those protocols or rates was out of the ordinary.

“We get errors because humans are involved,” Mueller said of all DNA testing. “One has to be aware of that when you use and evaluate” DNA.

But Mueller was not asked by the defense if he found that the labs made errors in handling or testing Rathbun’s DNA.

When under cross-examination by the prosecutor, Mueller examined DNA samples from blood and other evidence from crime scenes and was then asked whether it matched Rathbun’s DNA. Each time, he answered yes.

Since Rathbun’s arrest in November 2002, police and prosecutors have maintained that DNA evidence from crime scenes matched that taken by police from a saliva swab, and said that Rathbun has a rare genetic marker in his DNA that made it an even clearer-cut match.

The DNA has been critical because the victims’ descriptions of their attacker -- who always covered his face with a shirt or ski mask -- have sometimes varied dramatically in height, race and whether he had body hair.

In his opening argument, defense attorney Ed Barrett had told jurors that evidence would show that DNA testing is fallible and unconvincing when coupled with some victims’ descriptions that their attacker was Latino or 5 feet 6 when Rathbun is of Polynesian heritage and 5 feet 10.

The prosecution case featured DNA experts or analysts who used figures like “1 in septillion” to describe the odds that someone else also has Rathbun’s genetic fingerprint.

Mueller was the second of two DNA or forensic specialists who called such projections flawed because, for starters, there are not that many people on Earth through which such numbers could be borne out.

Dr. Elizabeth Johnson, a self-employed consultant who formerly worked at a private DNA lab in Ventura, testified Monday that errors via contamination, mishandling or mislabeling can occur. She said she was not asked by the defense to study Rathbun DNA reports.

To explain his calculations about likely error rates at the labs -- the crime labs for the Los Angeles County and Orange County sheriff’s departments, plus a private company in Northern California -- Mueller used baseball batting averages. He was trying to explain how to interpret one lab’s report that it had zero errors in 365 DNA tests. Mathematically speaking, he said, that lab did not have a zero error rate, which would require the lab to make no errors in a quadrillion tests.

Deputy Dist. Atty. Rich Goul asked if a player had that many at-bats and no strikeouts, would he not actually have had zero strikeouts?

“Up to that point, that’s correct,” Mueller said.

Closing arguments for both sides are expected today.