VISTA -- That a Fallbrook man killed his mother-in-law and teenage sister-in-law is not in dispute. But the question of whether it was murder or manslaughter when Jason Duane Cooper wielded the knife went to a North County jury Wednesday.

Before jurors began their deliberations, they spent the day in a Vista courtroom, listening to closing arguments.

Deputy District Attorney Kim Lagotta told the jury the evidence shows Cooper not only murdered the two victims, but tortured them with repeated stabbing during the attack in the Liebner family's Fallbrook home on April 26, 2006.

Jenna Liebner, 16, was stabbed 56 times, including a number of large slashes on her face. Her mother, Robyn Liebner, suffered 27 stab wounds. The attack on her was so severe, a piece of her spleen was found about a foot away from her body.

"This wasn't a random act of violence," Lagotta told the jury during her closing argument Wednesday. "This was a cold, calculated intent to kill."

Cooper's attorney, Wil Rumble, told the jury that the attack came in the heat of passion, and thus the deaths were voluntary manslaughter, not murder. According to testimony, Cooper himself called 911 after the slayings.

"Jason called 911," Rumble told the panel. "Torturers don't call 911. Murderers don't call 911."

Cooper, 27, has pleaded not guilty and not guilty by reason of insanity.

Any finding that Cooper is guilty of the killings -- whether murder or manslaughter -- will trigger a second phase of the trial, in which the jury will be asked to determine whether Cooper, who has a history of deliberately cutting himself, was insane at the time of the slayings.

According to testimony, Cooper first stabbed his young sister-in-law near the kitchen of the gated, ranch-style home in Fallbrook. The blood evidence, Lagotta said, shows that Jenna tried to crawl away from him, but Cooper followed and continued to stab her.

Crime scene photos show her bloody handprints on the carpet, and Cooper's bloody shoeprints following the same path. And, Lagotta said, it appears that she collapsed onto the floor five times as she tried to crawl away.

Lagotta said blood evidence shows Cooper then went to the bathroom and washed up. He left a knife in the bathroom sink, then grabbed a second knife from the kitchen to kill Robyn Liebner when she returned from feeding her horses, Lagotta said.

Also, the prosecutor said, Cooper wore latex gloves. She said he cut his hands as he repeatedly plunged the knife into his victims, and cuts in the gloves matched the cuts on his hands. Most of the blood on the latex gloves was Cooper's, apparently from his wounded hands, and a smaller portion of the blood was Jenna's. None of the blood on the gloves was Robyn Liebner's, suggesting that maybe he took them off before he attacked her.

Lagotta also said Cooper's blood was found in a trail throughout the house, as he apparently rummaged through drawers and files, possibly to find the combination to the family's gun safe. There is evidence, Lagotta said, that he fiddled with the handle and combination lock on the safe.

There has been some suggestion by the prosecution that Cooper killed his in-laws for inheritance money.

Rumble told the jury that the latex gloves are a red herring, and that perhaps they just happened to have been in Cooper's pockets when he visited the house to discuss medieval literature with Jenna.

He said an argument between his client and Jenna over books started the attack.

"All of the wounds show a frenzy, an impulsivity," Rumble said, adding that those are behaviors associated with the personality disorder from which doctors on both sides of the case said Cooper suffers.

There were differences in the mental health findings, though. The psychiatrist first introduced into the case when the court wanted a neutral evaluation of the defendant's sanity testified that Cooper suffers from no major mental illness. A psychologist for the defense, however, found that Cooper suffered from post-traumatic stress disorder, possibly brought on by severe abuse and neglect Cooper suffered as a child.

"It's not an abuse excuse," Rumble told the jury. "We're not asking you to excuse his behavior. … Yes, he's guilty of the killing. But he's not guilty of murder, and not guilty of torture."

Contact staff writer Teri Figueroa at (760) 740-5442 or tfigueroa@nctimes.com.