A book about a mafia serial killer who chopped up his victims may have inspired Aaron Carlino to kill his drug-dealer housemate, a Perth court has heard.
Carlino, who is on trial for murder, admits shooting and dismembering underworld figure Stephen Cookson, 56, in their East Perth apartment in December 2012, but claims he acted in self-defence after months of abuse.
Mr Cookson's body was dumped at sea a week after his death, and his head washed up on a Rottnest Island beach the following month.
Carlino, 30, told the West Australian Supreme Court on Wednesday that he had read a book called The Ice Man and another called The Hit Man, about "gangster style" killings.
He conceded under cross-examination by the prosecution that the books might "possibly" have given him the idea about how to kill Mr Cookson.
Carlino said he had no other option but to kill Mr Cookson, despite admitting he never sought police help.
"It wasn't really an option for me," he said.
Prosecutor Carmel Barbagallo repeatedly asked Carlino if he sought police assistance when he became afraid of Mr Cookson, including during a trip to NSW in which he was trusted to collect $500,000 for his mentor and could have approached police.
Carlino initially said he never considered talking to police, but under re-examination from his lawyer, said he "contemplated it briefly".
The court heard that while Carlino began working with Mr Cookson under a legitimate business agreement and believed he would help him pay off his $500,000 debt, he ended up being worse off financially due to failed ventures by Mr Cookson.
Carlino testified there were people trying to kill them as Mr Cookson's drug dealing activities took over and he then did not see the relationship as an opportunity to make money.
"I was seeing that as my life was in peril and in great danger," he said.
"The drug business wasn't doing anyone any favours."
Carlino also testified that he knew when he brought a gun into the apartment that it would be very difficult to get it out again without Mr Cookson noticing.
He said if Mr Cookson had seen the gun, he would have used it to kill him.
"I was in fear for my life," Carlino said.
While there was "some drug dealing afterwards", Carlino said he did not murder Mr Cookson to take over his business, insisting he did not have the contacts or potential to do the job.
He added that he could not start a new life on the back of killing someone and was glad, in hindsight, that he had been arrested.
His cousin, Yovan Joshua Gonzalez, is also on trial accused of interfering with Mr Cookson's corpse.
The trial continues.