'Fear' triggered man to shoot Cookson

Aaron Carlino was so intimidated by his convicted drug dealer housemate that he agreed to a threesome with the man whom he described as "like a father", a Perth court has heard.

Carlino has admitted to shooting and dismembering underworld figure Stephen Cookson 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, his head washing up on a Rottnest Island beach the next month.

Carlino told the West Australian Supreme Court on Tuesday that his relationship with the 56-year-old began in February that year after Mr Cookson agreed to pay off his $500,000 debt in exchange for his services.

Mr Cookson started off mentoring Carlino, teaching him about business and letting him live at his apartment.

But in June, the former semi-professional boxer bashed and threatened to gouge Carlino's eye out with a spoon after he confronted the drug dealer for gambling away money.

Mr Cookson said "you've f***ed up, I've got no choice, I'm gonna kill you," Carlino said.

Living with Mr Cookson was like "walking on eggshells" as the self-proclaimed murderer constantly threatened to hunt him down and kill him if he left, Carlino said.

Carlino said his friends and family were not allowed to visit, and Mr Cookson monitored all of his communications.

He was also made to sleep in a room with a glass wall, so Mr Cookson could see him from the couch he slept on.

On the one occasion Mr Cookson allowed Carlino's then-girlfriend to visit, Carlino said he was persuaded into having a threesome.

"If he pushed me to do something I would do it because I knew what the consequence was," Carlino said.

The court heard Carlino hoped to escape Mr Cookson because he was likely to be found guilty in a pending drug trial and sent to jail.

But Carlino became convinced Mr Cookson was going to murder him after he told him that they would flee to the bush together.

"Everything was coming to a head and I knew he was going to kill me," Carlino said.

"I realised it was a possibility that I would have to kill him."

Carlino said "fear" made him shoot Mr Cookson twice in the head at point-blank range with a rifle as he slept on the couch on December 15.

And he kept "putting off" dismembering the body because it was traumatic.

Carlino wrapped the body parts in plastic and buried them in the backyard of a Golden Bay property with his hands so the neighbours wouldn't hear.

He retrieved the parts a week later and dumped them at sea with his cousin, Yovan Joshua Gonzalez, who is also on trial accused of interfering with the corpse.

But Carlino said Gonzalez was "off with the fairies" on speed and didn't know the packages were body parts.

Carlino denied "absurd" accusations he wanted to take over Mr Cookson's drug dealing business, saying he started selling small amounts of ecstasy and cannabis after the killing because people kept calling him.

Carlino's evidence continues.