An air conditioning repairman charged with murdering a Chicago-area teenager and two California women, one the ex-girlfriend of actor Ashton Kutcher, would “watch, shadow, stalk and hunt down” his victims before fatally stabbing them for sexual pleasure, a Los Angeles prosecutor said during opening statements Thursday. Michael Gargiulo’s trial began with a prosecutor outlining the California murders for jurors, calling the defendant “the boy next door killer” and his crimes “the methodical and systematic slaughter of women.” “What you will hear is that Michael Gargiulo for almost 15 years was watching, always watching,” prosecutor Daniel Akemon said. “And his hobby was plotting the perfect opportunity to attack women with a knife in and around their homes.” Gargiulo, 43, has pleaded not guilty to two counts of murder and an attempted-murder charge stemming from attacks in the Los Angeles area between 2001 and 2008, including the death of Kutcher’s former girlfriend, 22-year-old Ashley Ellerin. Gargiulo was arrested in 2008 after DNA evidence linked him to one of the killings and a non-fatal attack. He was separately charged with killing an 18-year-old Glenview, Illinois, woman whose father found her fatally stabbed on their family’s doorstep, house key still in hand. Prosecutors are seeking the death penalty. Gargiulo’s attorney, Daniel Nardoni, reminded jurors during his opening statement that his client is presumed innocent and said other men had better access or motive in the killings. He also pointed out that no murder weapon has been found and no DNA evidence connected Gargiulo to the killing of Ellerin. Gargiulo’s trial is expected to take six months. Kutcher, who is married to Mila Kunis, is among the witnesses expected to take the stand. Kutcher’s ex-girlfriend was found dead in 2001 in her Hollywood Hills home. Kutcher told police he went to pick up the fashion student-model for a post-Grammy Awards party, but she did not answer the door. He checked a back window and spotted what he thought were red wine stains on the carpet and then left. Her body was discovered the next day by a friend. Another victim in the case, 32-year-old Maria Bruno, was found stabbed to death in her apartment in suburban El Monte in 2005. Her breasts had been cut off. One victim survived a stabbing attack in her Santa Monica apartment in 2008. Gargiulo was a neighbor of each victim at the time of the attacks. The teenager killed in Illinois, Tricia Pacaccio, lived just down the street from Gargiulo in suburban Glenview. Gargiulo was a friend of her brother’s and 17 at the time Pacaccio was stabbed to death on her front porch. Later police said DNA collected from Pacaccio’s fingernails matched Gargiulo.