In the series finale, David Pearce faces a jury for his alleged role in the deaths of Christy Giles and Hilda Marcela Cabrales-Arzola, and the alleged sexual assault of seven other women. We speak to the lead prosecutor of the case, L.A. County Deputy District Attorney Catherine Mariano, and James Queally from the L.A. Times to break down the trial.

The Hollywood Ripper story begins in Glenview, Illinois - an unincorporated suburb of Cook County, where 18-year old Tricia Pacaccio was just finishing high school. Tricia attended a road rally with her friends, one of the last times they would get to see each other before leaving for college. When she returned home, she was attacked at her side doorstep and stabbed over a dozen times. Her father found her body the next day, and the Cook County Sheriff's Office began to investigate. After years of finding no leads, a new investigative team began to zero in on one of Tricia's neighbors - Michael Gargiulo - who grew up with Tricia's brother Doug. Even after finding himself in trouble with the law, police couldn't convince Gargiulo to provide any information about Tricia's murder, or what he may have known about it. Eventually, he moves to Hollywood, California, where another woman was murdered just blocks away from his house.

Seven years after Tricia Pacaccio's murder, Cook County's Sheriff's Office were now treating it as a cold case. A new investigative team submitted Tricia's fingernail clippings taken from the crime scene as DNA evidence, hoping to get a match. Meanwhile, Michael Gargiulo had moved to Hollywood, where he met 22-year-old Ashley Ellerin, who lived a few blocks from his house. After introducing himself as an air conditioning repair man, "Mike" would eventually start showing up at some of Ellerin's parties uninvited. Ashley was living a glamorous Hollywood lifestyle, partying with some famous actors like Vin Diesel and Ashton Kutcher. The night of February 21, 2001, she had plans to meet Kutcher for drinks after the Grammy Awards, but she never made it there. Ashley was murdered inside her apartment, stabbed 47 times and nearly decapitated in a brutal attack with a knife. We speak with Detective Tom Small of the L.A.P.D., who investigated the case, and began searching for a man who was only known by Ashley's friends as "Mike the furnace guy".

Cook County detectives are looking for Michael Gargiulo in California, and connect with L.A.P.D. homicide detective Tom Small to help locate him. Armed with a search warrant, detectives track him to an apartment listed under his girlfriend's name, and arrest him. They submit his DNA for testing and get a match with the DNA collected from Tricia Pacaccio's fingernail clippings. When the Cook County State's Attorney's office is presented with the evidence, they decide not to charge Gargiulo due to the possibility of the DNA being obtained by "casual contact". We speak with DNA expert Kristen Mittelman and former L.A. County prosecutor Joshua Ritter on the decision by Cook County's State's Attorney not to prosecute Gargiulo. Plus, Tom Small tells us how the Pacaccio family reacted to the news.

After Cook County's State's Attorney chose not to prosecute, Michael Gargiulo is once again a free man. He moves into an apartment in El Monte, California with his girlfriend, where a 32-year-old woman named Maria Bruno moves in across the complex. Less than two weeks after she moves in, Maria Bruno is killed. Her estranged husband, Irving, finds her stabbed, mutilated, and left for dead in her own bed, just hours after the two had been out the night prior. In a chilling 911 call, Irving describes the scene to police. Mark Lillienfeld, a detective with Los Angeles County Sheriff's Department, is assigned to the case. We speak to Det. Lillienfeld about the crime scene, witness statements from people who lived in the apartment, and a crucial piece of evidence left at the crime scene: a blue medical bootie with drops of blood on it.

With no suspects in Maria Bruno's murder, L.A. County Sheriff's Deputy Detective Mark Lillienfeld continues the search. Michael Gargiulo marries, then moves to Santa Monica, California, with his wife. Across the alleyway, 26-year-old Michelle Murphy lived in an apartment nearby. One night, Murphy woke up with a man on top of her, stabbing her repeatedly with a knife. She manages to kick off the attacker, who cuts himself in the struggle and flees the apartment. When police arrive, they find blood at the crime scene that matches Michael Gargiulo, and he's eventually arrested for the attack. When L.A. County Sheriff's detectives who were investigating Maria Bruno's murder find out, they search Gargiulo's old apartment in El Monte and find a key piece of evidence. With Gargiulo now in custody, CBS 48 Hours airs a special about Tricia Pacaccio's murder in Cook County, which leads to a break in the case. We speak with CBS correspondent Maureen Maher about the special, plus former Santa Monica Police lieutenant Darrell Lowe about the attack on Michelle Murphy, and Mark Lillienfeld details the search of Gargiulo's El Monte apartment and a controversial undercover operation conducted while Gargiulo was in custody.