MARTINEZ, Calif. — Blood bags and a brief appearance by a psychic detective gave murder defendant Susan Polk a jumpstart Monday as she began the seventh week of her defense case.

"My question upon reading the autopsy report was: What killed him? What caused this death?" defense expert witness Roger Clark testified Monday about Polk's 70-year-old husband Felix Polk.

Clark, a retired Los Angeles County sheriff's lieutenant who was called by Polk as an expert in crime scene analysis and police procedures, agreed with a defense medical expert's opinion that Felix died from his blocked arteries and not his multiple stab wounds and blunt force head trauma.

Clark reviewed bloody crime scene photos and did water-pouring tests on the floor where Felix's body was found to conclude that the victim also did not "bleed out" or bleed to death.

A healthy person, Clark told jurors, walks around with a total blood volume of roughly 12 pints.

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Clark held up a clear plastic IV-type bag filled with about 2 pints of clear fluid. A typical blood donation, Clark said, is 1 pint, or half the bag.

He surmised that Felix lost perhaps 1/10 of the bag from a stab wound to his chest.

Felix's total blood loss, Clark opined, was 1 to 2 pints. But for death to occur, he said, a person would have to lose about 4 pints, or two of the same IV bags, worth of blood.

Polk, 48, is accused of stabbing her psychologist husband to death with a paring knife in October 2002 in the poolside cottage of the couple's $1.85 million Orinda home during a nasty divorce battle. Polk's youngest son, Gabriel, testified that she openly talked about killing his father.

Polk initially denied any knowledge of her husband's death, but later claimed she acted in self-defense after he attacked her first with the blade. Polk says her husband mentally and physically abused her since the age of 14, when she became his patient.

She is in custody and faces 25 years to life if convicted of first-degree murder.

'Sprinkled blood around'

Clark said that the location of Felix's "random" stab wounds told him that Polk had no "intent to finish the job."

He agreed with prosecutor Paul Sequeira that the gaping defensive wounds on the inside of Felix's hands appeared to be from Felix's attempts to grab the blade. Defensive wounds, Clark said, bring up the issue of whether a person was "caught by surprise" or didn't have time to react.

He also agreed that there was blood spatter and blood drops that fell beyond the contained area where Polk says the stabbing took place but argued that it could have resulted from Felix flailing his arms or his blood dripping off Polk's body.

He refused to concur, however, with Polk's theory that detectives tainted the crime scene and "sprinkled blood around."

"That is a felony. It's called obstruction of justice. I didn't see that," Clark told Polk during redirect testimony. "We're talking about something that would require the cooperation of a number of officers. I didn't see it."

Polk has accused officers of pouring water on her dead husband's head to make the bloody scene appear bloodier, and stealing a shoe from her closet, dipping it in blood, and stamping her prints around the body.

"Susan, I ..." Clark paused. He appeared uncomfortable with her questioning. "Can a scene be tampered with? Of course it can. If officers wanted to do something like that, it would be reprehensible."

"Haven't there been trials where it's been established that that was done?" Polk asked.

"I can't remember a trial like that," Clark said.

"The O.J. Simpson trial?" Polk shot back.