VISTA, Calif. -- A man accused of fatally stabbing a Vista mother four years ago was seen in her backyard, and authorities later recovered DNA from both her and the defendant on a knife, a prosecutor said Monday, but a defense lawyer said his client "is not the killer."

Derlyn Ray Threats, 28, is charged with murder and special circumstance allegations in the Sept. 1, 2005, death of 24-year-old Carolyn Rebecca Neville, who was stabbed 80 times after returning home from taking her 6-year-old son to school.

Neville had misplaced her house keys and left the door open, authorities said.

Investigators found an unplugged X-Box game console and a suitcase full of DVDs in the residence, leading them to believe Neville interrupted a burglary.

If convicted, Threats faces the death penalty or a no-parole life prison term.

During his opening statement at trial, Deputy District Attorney Patrick Espinoza said that sheriff's deputies had responded to calls of a woman screaming in the 1200 block of Diablo Place.

"(The deputies) see the defendant standing in Carol Neville's backyard," and they chased after him after he climbed a fence, the prosecutor said.

"Two houses down, (Threats) drops a knife that's recovered later," Espinoza told the jury. "They do some testing. Carolyn Neville's DNA is found on that knife. It's a mixture. Derlyn Threats' DNA is found on that knife."

Espinoza said Threats was detained at gunpoint and in his pants deputies found a stun gun, the wooden handle of a hammer that was missing its head and a bloody blue bandana.

The victim's blood was on the handle of the hammer and scrapings under the defendant's fingernails contained the victim's DNA, the prosecutor said.

"This was a very torturous killing," Espinoza said. The defendant had a "a sadistic purpose" and wanted to "inflict extreme pain on Carlyon Neville," according to the prosecutor.

Espinoza said there was so much blood throughout the house that it took several days for evidence technicians to process the scene.

He said a neighbor heard a man yelling for someone to get back inside and blood spatter was found on the front door jam. The only way that could happen is for the front door to be open, Espinoza said.

"That blood evidence proves she almost made it out," the prosecutor said.

But defense attorney James Weintre told jurors in his opening statements that somebody else killed the young mother.

"Mr. Threats is not the killer," Weintre said.

The attorney noted that a hole on a window screen in the victim's house shows the defendant actually went out through the front yard and not the back yard.

Weintre said a steak knife with the victim's blood on it was found in the front yard of a house two doors down.

The attorney said one of the first deputies on the scene called on the radio to describe a 6-foot-2-inch man with dark gloves and a motorcycle helmet.

None of those descriptions matched Threats, who is 5 feet 9, Weintre told the jury.

The responding deputy was "specific, he was detailed, with no wavering," the defense attorney said.

Weintre said there was very little blood on Threats' clothing and he had no motive to kill Neville.

The attorney said Threats robbed a Taco Bell at age 15 and at age 21 took a gun from a Marine armory.

Testimony is expected to run through November in the Vista courtroom of Judge K. Michael Kirkman.