MARTINEZ, Calif. — Gothic imagery, dark poetry and an obsession with cult murders imbued the mind of a 17-year-old former Boy Scout who is accused of brutally killing 52-year-old Pamela Vitale, prosecutors said during opening statements Thursday in the teen's first-degree murder trial.

"It wasn't Goth, it wasn't even death, it was murder," prosecutor Harold Jewett said of the nature of writings and drawings that investigators found in a search of the boy's bedroom.

The defendant, Scott Dyleski, has pleaded not guilty to the murder of Vitale, a mother of two and former Bay Area high-tech executive who was married to prominent California defense attorney Daniel Horowitz.

Dyleski is also charged with the special circumstance of murder during a burglary.

Dyleski allegedly disguised himself in a black ski mask, gloves and trench coat before entering Vitale's home and making a surprise attack on his neighbor, shortly after 10 a.m. on Oct. 15, 2005.

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"Scott Dyleski is not a killer and he did not commit this crime," said his attorney, public defender Ellen Leonida, who promised the jury that DNA evidence and an inconsistent timeline will show the boy had nothing to do with Vitale's murder.

Dyleski had multiple scratches and marks on his body and face when he was examined by police. Dyleski says he received them during a nature walk.

A member of Dyleski's household will testify, according to Leonida, that the time was 9:26 a.m. — before Vitale's death — when the teen returned from his walk.

Leonida tried to bring Dyleski's gentle qualities to the forefront. She described him as a kind kid, a helpful babysitter, a former Little Leaguer and Frisbee team member. He may have enjoyed dark music and dress, Leonida told jurors, but he cared deeply for life, and was so harmless that he didn't eat meat or wear leather.

Prosecutor Jewett portrayed the teen as a ruthless killer who stunned and attacked Vitale, leaving her with "26 separate devastating wounds to the head," dislodged teeth, broken fingers.

"She fought as valiantly as she could, but the attack continued," Jewett said.

Internal bleeding in Vitale's brain led to her immediate death, Jewett said, but even after she died from her head injuries, the attack continued.

Vitale was stabbed so viciously in her abdomen, Jewett said, that her intestines were exposed. And then the killer carved a symbol into her back.

"Mr. Dyleski was big into symbols. He signs his name and puts his symbol on his artwork," Jewett said.

The prosecutor drew a symbol on a white piece of butcher paper that represented the signature Dyleski allegedly carved into Vitale's back, an H-shaped symbol with an extended T-bar.

Vitale's children, Marisa and Mario, sat in the front row, quietly crying and holding each other. Horowitz sat two rows back with his sister and wore a pained expression while shaking his head.

Dyleski wore a crisp white dress shirt, tan khakis and a gold tie Thursday. His mid-neck-length black hair was slicked back.

During pretrial hearings in March, the defendant was engrossed in writing on a yellow legal pad, barely looking up at witnesses. But during opening statements Thursday, he watched the prosecutor's every move and listened intently.

Jewett offered jurors small details about Vitale's life to remind them that she was more than a tragic murder victim depicted in crime scene photos.

Vitale was born in Texas, grew up in Minnesota and raised two children as a single mother in California, Jewett said. She was a stewardess for Pan Am airlines, then worked for Hewlett Packard and moved up to an executive position at a high-tech Bay Area firm.

She later met and fell in love with Horowitz, and the two had been married almost 11 years when she was killed. They lived in a modular home on their 12-acre hilltop property while Vitale oversaw construction of their dream home: A European-style mansion with a vineyard.

Jewett described how Horowitz discovered the horrific crime scene after coming home from a long day of working on his newest case — the defense of Susan Polk, on trial for the murder of her husband — and approached the front door to their home.

"He knew something was wrong, because he saw blood smears," Jewett said. "And then he opened the door and saw his wife."

Vitale's body was in a fetal position near the front door, a pool of blood around her head.

"'No, Pamela, no! No, please! No!'" Jewett reenacted for jurors the sounds of Horowitz's screams as later described by neighbors who called 911. "Over and over again, his voice echoing down the canyon."

Jewett told the jury that he planned to call some 40 witnesses, including Dyleski's best friend, who tipped off police to the pair's marijuana-growing scheme that allegedly was the impetus for Dyleski's run-in with Vitale; the defendant's girlfriend, whom he allegedly asked to keep a red backpack filled with evidence; and his own mother, a reluctant witness who agreed to cooperate in exchange for escaping prosecution herself after she destroyed clothes, notes and other evidence.

Prosecutors also plan to offer the jury about 100 exhibits, including DNA evidence, bloody clothing, footprints, glove prints, fingerprints, and journal writings and drawings found in Dyleski's room.

"Listen carefully, in particular, to the DNA evidence," Leonida told jurors, alleging that a third DNA profile was found at the crime scene.

"Scott Dyleski had no motive whatsoever to commit this crime," Leonida said.

Dyleski, who is being tried as an adult, faces a maximum sentence of life in prison without parole if he is convicted.

Jurors will return Monday for the start of testimony.