Investigators reveal Golden State Killer's possible motive for rapes, murders

The motivation for the infamous Golden State Killer to rape and murder dozens of victimsmay have prompted by his hatred of his ex-fiancee, investigators say.

Joseph DeAngelo, 72, was arrested at his Californian home earlier this week after DNA linked to the Golden State Killer from the 70s and 80s was also linked to some of his crimes.

DeAngelo is suspected of at least 12 murders and 45 reapers over three decades, reports News.com.au.

Joseph James DeAngelo, 72, who authorities suspect is the so-called Golden State Killer. Photo / AP

Paul Holes, an investigator who has spent years looking in to the case, said that a critical clue to linking DeAngelo to the attacks was that he yelled out 'I hate you Bonnie' during one of his first alleged rapes, The Mercury News reports.

It is reported that DeAngelo was once engaged to a woman named Bonnie.

'Most certainly if he's making the statement, "I hate you, Bonnie," while he's attacking another female, he is what we call an anger retaliatory rapist. Instead of directing his anger at what's making him angry, he's directing it sideways onto someone else to be able to satisfy that anger,' Mr Holes said.

'I do believe that's what happened here. I don't know what made him that way, but you've got to think Bonnie dumped him, he's not happy about that, he still had feeling for her, who knows? But something along those lines must have happened.'

Ski masks the Golden State Killer used on his victims. Photo / AP

Mr Holes has helped test DNA from the various crime scenes and tie them all together since 1994.

'We always thought there was a Bonnie significant in his life, it could be a mother, a wife, a girlfriend, a childhood crush,' Mr Holes said.

Realising that DeAngelo's ex-fiancee was named Bonnie and the DNA match helped police close in on the arrest.

The "quiet" grandpa from Citrus Heights, California, carried out his attacks in sadistic fashion.

Authorities probe the backyard of the home of murder suspect Joseph DeAngelo. Photo / AP

His most depraved tactic included tying up men and piling dishes on their backs while he raped their partners. He told them that if the plates tumbled to the ground, he would kill them both.

Police say he entered homes up and down the coast wearing ski masks and armed with a gun and a knife. He woke his victims by shining a flashlight in their eyes and spoke through gritted teeth to disguise his voice.

Police used DNA to finally track him down and tie him to the crimes but refused to give specifics about how it was collected or matched to the suspect. They admitted that despite decades of work, Mr DeAngelo's name had not been on authorities' radar before last week.