An obsessed stalker who placed a tracker device on his ex-girlfriend's car faces a "very substantial minimum term" in jail for murdering her, a judge said.
Shana Grice, 19, was found with her throat slashed in her smoke-logged bedroom at the bungalow she shared with two housemates in Brighton, East Sussex.
Her jilted ex-boyfriend, Michael Lane, 27, waited until she was home alone before murdering her last August 25 after she decided to rekindle a relationship with her ex-boyfriend, Ashley Cooke.
Miss Grice's family criticised police, saying they believed her murder could have been prevented if officers had listened to her fears about Lane.
Her mother Sharon Grice said in a victim impact statement read on her behalf: "We brought Shana up to respect authority and to always respect the law.
"We firmly believe her murder could have been prevented if her fears had been listened to and taken seriously by the police."
Police received at least four reports about Lane's behaviour towards Miss Grice, but on one occasion she ended up with a fixed penalty notice for wasting police time.
Sussex Police apologised to Miss Grice's family and referred themselves to the Independent Police Complaints Commission (IPCC), which has launched an inquiry.
Deputy chief constable Bernie O'Reilly said: "When we looked at the circumstances leading to Shana's murder, we felt we may not have done the very best we could."
A two-week trial at Lewes Crown Court heard that Lane refused to accept their break-up and decided no one else could be with her, telling a friend: "She'll pay for what she's done."
In the months before she died, Lane stalked Miss Grice, the trial heard. He put a tracker device on her car and received notifications via a phone app every time it moved.
Mechanic Lane, of Thornhill Rise, Portslade, claimed he innocently found her body and left her home without raising the alarm as he was in shock.
But as jurors convicted him of murder after just over two hours of deliberation on Wednesday, friends and family broke into cheers and claps.
Lane's defence counsel Simon Russell Flint QC said there were "no mitigating factors". Judge Mr Justice Green will sentence Lane at 10.30am.