The case garnered national attention as one of the victims, Ashley Elrin, was planning to go on a date with Kutcher on the night of the murder. The actor testified during the trial.
Gargiulo maintains his innocence but prosecutors paint an image of him as a murderer, who introduces himself as a friendly neighbor and handyman before breaking into their homes and stabbing them to death.
He was also known as “The Boy Next Door Killer”.
Los Angeles Superior Court Judge Larry P. Fiedler called his crimes “vicious and appalling” at sentencing on Friday, as family members of the victims wept.
Throughout the day’s hearing, Mr. Fiedler said, “Wherever Mr. Gargiulo went, death and destruction followed him.”
Gargiulo was convicted in 2001 of the murder of 22-year-old fashion design student Ashley Allerin while she was preparing to go out with Kutcher.
Testifying at the trial, Kutcher said he was late to pick up Ms. Alerin, who did not answer her door.
When he looked inside he saw blood stains which he thought had spilled alcohol. Ms Allerin was found with 47 stab wounds.
Her father, Michael Allerin, who had visited her hours before his daughter’s death, spoke at the hearing of his family’s suffering and the long awaited justice.
He said he was tempted to imitate his wife Cynthia’s “mourning screams and groans after discovering Ashley’s murder”.
He said his death “marks the beginning of a changed, low, heartbreaking life”.
Gargiulo was also convicted of murdering 32-year-old Maria Bruno, mother-in-law of four, in her home in El Monte, east of Los Angeles, in 2005. Ms Bruno had her breasts cut out and her implants removed.
He was also found guilty of the attempted murder of Michelle Murphy in 2008.
Ms. Murphy confronts her in her Santa Monica apartment, forcing her to flee and leaving behind traces of blood that led to her arrest for the other two murders. She was the main witness in the trial.
Before sentencing, Ms Murphy said in court: “To this day, spending the night alone creates a world of fear in me.”
She cried as she talked about meeting the families of the two women who had not survived their attacks.
“How is it fair that the act of one person can destroy the lives of so many?” he said.
Gargiulo is a former air conditioner and heater repairman, bouncer and aspiring actor. Speaking before the sentencing, he angrily complained that his lawyers had prevented him from taking a stand in his defence.
“I am unfairly and unjustly going to the death penalty,” Gargulo said. “I wanted to testify and my fundamental choice was blocked.”
Gargiulo is expected to be extradited to Illinois in connection with the 1993 murder of Tricia Pacacio in her hometown of Glenview.
In 2011, the Cook County state attorney charged him with first-degree murder of Ms. Pacchio.
His California trial allowed prosecutors to present extensive evidence from that case as they sought to establish a pattern and present Gargiulo as a serial killer. Investigators believe there may be more victims.
California has not executed anyone since 2006 and a Democratic governor Gavin Newsom As long as he is in office, the execution has been stopped.
The courts continue to operate on the assumption that one day the executions will resume.
With reporting by The Associated Press