MARTINEZ, Calif. — An expert witness testifying on behalf of murder defendant Susan Polk told jurors Monday that he could no longer be a neutral witness because "there was an injustice being carried out" and Polk was "being held on false charges."

"You haven't sat here and heard all the evidence. You don't know if she's being held on false charges," Assistant District Attorney Paul Sequeira said to the witness, retired Texas forensic pathologist Dr. John Cooper.

"I see that the autopsy evidence exonerates her," Cooper said.

Cooper previously testified that Polk acted in self-defense when she stabbed her husband with a paring knife in October 2002. He said that Felix Polk's injuries, including 27 stab wounds and blunt force trauma, were "relatively trivial" and not immediately life-threatening.

"Certainly it's a contributing factor," Cooper said of the victim's injuries. "I believe it is sound logic to say if he weren't involved in an altercation, he wouldn't have died."

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But Cooper stood by his opinion that Felix died of a heart attack — as evident by blocked arteries — while committing an "aggressive" and "angry" attack on his wife.

The county's forensic pathologist autopsied the victim and previously testified that Felix died from his injuries and that his hardened arteries simply made it harder for him to fight off his attacker.

Felix, according to testimony, was 5 feet 9 inches and 170 pounds at the time of death. Polk was 5 feet 4 inches and about 110 pounds.

Susan Polk

Polk, 48, is acting as her own lawyer. She is expected to testify this week that she sprayed her 70-year-old psychologist husband with pepper spray before wrestling the knife away from him. Police photographs, taken a day after the incident, show small red marks around her eyes and a single red mark on her shoulder.

Sequeira noted that Susan Polk had no knife nicks on her body.

"I object!" Polk said. "I did have injuries. They were relatively light compared to my husband. My crime is that I survived."

"The odds were definitely against her," Cooper said. "It's unbelievable that a woman that size would attack a full-grown man — the chances of her surviving are miniscule."