A man dubbed "The Boy Next Door Killer" will face the death penalty after he was found guilty of two murders and an attempted murder by a jury in Los Angeles.
The actor, who was a 23-year-old rising star on That '70s Show when Ellerin was killed, testified at trial that he arrived late for his date with Ellerin.
Now 41, he said looked into her house when there was no answer at the door, and saw what he thought were wine stains before leaving.
Gargiulo was convicted of the 2005 murder of 32-year-old Maria Bruno and the 2008 attempted murder of Michelle Murphy, who testified during the trial's penalty phase that she lived in fear for years after the attack.
Murphy fought when she was attacked in bed by the 43-year-old in her Santa Monica flat.
She testified that she "barely even slept" in the weeks and months after the attack.
"I feared the nighttime and going to bed. I still slept with the lights on for a long time." she said.
Prosecutors called Gargiulo "The Boy Next Door Killer" because he lived near all the victims. Ellerin had become an acquaintance before the attacks.
Investigators said he cut himself during the attack on Murphy and left a trail of blood that allowed prosecutors to tie him to the other cases, including a 1997 killing in Illinois for which he is still awaiting trial.
Ellerin's mother, Cynthia Ellerin, and other victims' family members also testified during the penalty phase.
"I fell to my knees on the floor and started crawling around the bedroom on my hands and knees like an animal, screaming," she told jurors. "I ache to hold her. I ache to hear her voice, to hug her. But that's not going to happen."
Gargiulo showed no reaction as the court clerk read the death sentence at the brief hearing.
His attorney Daniel Nardoni said outside court that he was angered and disappointed by the decision. Jurors also could have recommended life in prison with no possibility of parole.
"You don't kill people that are mentally ill," he said. "It's just a matter of humanity. There's a different kind of punishment for the mentally ill. It's called life without parole."
Defence attorneys and a psychologist said in court that Gargiulo has dissociative personality disorder, formerly known as multiple personality disorder.
California has not executed anyone since 2006, and the state's governor, Gavin Newsom, earlier this year halted executions for as long as he is in office.
Courts have been proceeding on the assumption that they may one day resume.