LOS ANGELES (CBSLA/AP) – Actor Ashton Kutcher testified for about 40 minutes Wednesday morning in a downtown Los Angeles courtroom in the ongoing trial of the serial killing suspect known as the “Hollywood Ripper,” who is accused of brutally murdering three women, one of whom was dating Kutcher when she was killed back in 2001.

Michael Gargiulo, 43, an air conditioning repairman, is charged with murdering a Chicago-area teenager in 1993 and two women in the Los Angeles area in 2001 and 2005. He is also charged with stabbing a woman in Santa Monica in 2008, but she escaped and survived.

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Ashton Kutcher testifies on May 29, 2019, during the trial of Michael Gargiulo. (Getty Images)

Gargiulo was a neighbor of each victim at the time of the attacks. He has pleaded not guilty to two counts of murder and one count of attempted-murder. Prosecutors are seeking the death penalty.

Kutcher’s then girlfriend, 22-year-old Ashley Ellerin, was murdered on Feb. 21, 2001, in her Hollywood Hills home. She had been stabbed 47 times.

Kutcher had previously told police he went to pick up the fashion student-model for a post-Grammy Awards party that night, but she did not answer the door.

From the witness stand, the 41-year-old Kutcher told the jury it was hard to recall many details. He said he had exchanged a few phone calls with Ellerin that day and was running late for their dinner.

Michael Gargiulo appears in court for opening statements in his murder trial on May 2, 2019, in Los Angeles, Calif. (Getty Images)

He said that he looked into the window at Ellerin’s home and saw what he believed were wine stains before leaving, thinking the fashion design student had already gone out for the night.

Kutcher said he told detectives the next day he knew his fingerprints were on the door and he was “freaking out.” He testified he had tried to push open the door to yell inside to get Ellerin’s attention. Defense attorney Daniel Nardoni responded that Kutcher was not a suspect.

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In 2005, Gargiulo is accused of killing a young mother, 32-year-old Maria Bruno, who lived in the same El Monte apartment complex as him. Her breasts had been cut off.

Victim photos are shown as Michael Gargiulo appears in court for opening statements in his murder trial on May 2, 2019 in Los Angeles, California. Gargiulo is charged in the stabbing deaths of two women, one of whom dated actor Ashton Kutcher, and with attempted murder of a woman during a robbery at her home. (Al Seib-Pool/Getty Images)

In 2008, Gargiulo moved to Santa Monica, where prosecutors say he tried to stab another woman, 26-year-old Michelle Murphy, to death. Murphy, also a neighbor of Gargiulo, escaped and survived.

“What you will hear is that Michael Gargiulo for almost 15 years was watching, always watching,” prosecutor Daniel Akemon told the jury during opening statements. “And his hobby was plotting the perfect opportunity to attack women with a knife in and around their homes.”

(Getty Images)

Gargiulo’s trial began May 2 and could last 6 months.

In 1993, 17-year-old Tricia Pacaccio was stabbed to death on the front porch of her suburban Chicago home. Pacaccio lived just down the street from Gargiulo, who was a friend of her brother’s.

According to CBS News, Pacaccio’s murder was unsolved until 2011, when two witnesses came forward after watching a “48 Hours Mystery” report on the case. Within a few weeks, Gargiulo was indicted.

Once the L.A. trial is over, Gargiulo will be sent back to Illinois to face murder charges in Pacaccio’s death.

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(© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)