What to know about the 'Hollywood Ripper' 'thrill killer' trial of Michael Gargiulo

A multiple-murder trial unfolding in a Los Angeles courtroom has all the elements of a Tinseltown thriller with a suspect alleged to be the "Hollywood Ripper" and a star prosecution witness who just happens to be a movie star.

The defendant, Michael Gargiulo, 43, a former air-conditioner repairman, is charged with the stabbing slayings of two women -- Ashley Ellerin and Maria Bruno -- and the attempted murder of a third woman, Michelle Murphy, who testified that she fought him off in 2008 when he allegedly broke into her Santa Monica apartment and attacked her with a serrated knife in her bed.

Gargiulo has also been charged with the 1993 stabbing death of a suburban Chicago teenager and will face another murder trial there once his Los Angeles case wraps up.

He has pleaded not guilty to all of the charges in the California cases. He has not yet entered a plea in Illinois.

"I'm 100 percent innocent," Gargiulo told CBS's "48 Hours" in a 2011 jailhouse interview.

Los Angeles County prosecutors alleged that Gargiulo is a "serial, psychosexual thrill killer," who targeted, stalked and attacked women over a span of 15 years.

"His hobby was plotting the perfect opportunity to attack women with a knife in and around their homes," Los Angeles Assistant District Attorney Daniel Akemon said during his opening statement in the high-profile trial earlier this month.

On Wednesday, actor Ashton Kutcher took the witness stand in the downtown Los Angeles courtroom and testified about going to the Hollywood Hills home of one of the victims, Ellerin, 22, a model and fashion design student, to pick her up for a date on the night prosecutors alleged she was fatally stabbed 47 times by Gargiulo.

Kutcher, 41, testified that on Feb. 21, 2001, he had planned to go out for dinner and drinks with Ellerin and was late to pick her up when he arrived at her home and knocked on her door.

"There was no answer," Kutcher, who then was still a cast member on the Fox sitcom "That '70s Show," testified. "I knocked again and once again no answer. At this point, I pretty well assumed ... she had left for the night and that ... I was late and she was upset."

He said the lights were on inside Ellerin's home and that he looked through a window before he left.

"It was a little bit of a mess," he testified. "I saw what I thought was ... red wine spilled on the carpet. I didn't think anything of it."

Prosecutors said that the red liquid Kutcher mistook for wine was actually Ellerin's blood.

The actor testified that when he learned of Ellerin's slaying the next day, he contacted police immediately, fearing he would become a suspect in the homicide because he left his fingerprints on the victim's front door.

“My fingerprints are on this door and I was freaking out,” he said, adding that he told homicide investigators every detail he could remember of that night.

"Don't worry, you're not a suspect," Gargiulo's defense attorney, Daniel Nardoni, told Kutcher during his cross-examination of the actor.

In his opening statement, Nardoni asked jurors to "keep an open mind" and reminded them that Gargiulo is presumed innocent.

“I can assure you today, Mr. Gargiulo ... denies killing Ashley Ellerin and Maria Bruno … and Tricia Pacaccio,” Nardoni told the panel.

Bruno, a married 32-year-old mother of four, was found stabbed to death on Dec. 1, 2005, in her apartment in the L.A. suburb of El Monte. Prosecutors said Bruno was not only stabbed 17 times, her body was mutilated.

The first witness prosecutors called in the case, and possibly the most important, was Michelle Murphy, who testified that on April 28, 2008, she was awakened in her bed by a man straddling her and stabbing her repeatedly.

“I was trying to hold the knife to get some leverage to keep it from stabbing me,” Murphy, who was 27 years old when she was attacked, testified.

“Why are you doing this?” she recalled asking the attacker.

She testified that he eventually gave up, said "I'm sorry" and ran from her residence.

Prosecutors said a trail of blood found outside Murphy's home matched DNA from Gargiulo.

Less than two months after Murphy was attacked, police arrested Gargiulo.

In 2011, the Cook County, Illinois, State's Attorney charged Gargiulo in the cold-case killing of Tricia Pacaccio, 17, Gargiulo's former neighbor in the Chicago suburb of Glenview, who was stabbed more than 40 times on August 14, 1993, and found dead on the backdoor stoop of her home.

Illinois prosecutors are planning to try Gargiulo in Pacaccio's murder, but must wait until his Los Angeles trial is over.

Gargiulo's Los Angeles trial is scheduled to last up to six months and more than 100 witnesses are expected to testify.