The president of a white supremacist group says it was one of its associates, and not him, who murdered the partner of his lover in what he described in a Perth court as an "animal-like" attack.

Robert Edhouse, the president of the group Aryan Nations, is giving evidence in the Supreme Court as part of his defence against the charge of murdering Alan Taylor, 42, as he lay in his bed at his Girawheen home in April 2016.

It is alleged Mr Taylor's partner and mother of his young son, Melony Attwood, 37, planned the murder with Mr Edhouse, who was her lover and also living at the house.

The prosecution's case is that the murder was committed so Ms Attwood could access Mr Taylor's life insurance.

Another member of Aryan Nations, Corey Dymock, is also on trial accused of taking part in the murder, while a fourth person, an associate of the group who cannot be identified, admitted his part in the killing and has been jailed.

State prosecutors allege Mr Taylor was attacked with a hammer by Mr Edhouse, Mr Dymock and the associate, while Ms Attwood turned up the music to drown out the sound of what was happening before ransacking the house to make it look like a burglary.

They say the four then went to see the film The Jungle Book to try to create false alibis.

Defendant 'stunned' by 'surreal' murder

In his evidence, Mr Edhouse, 22, maintained it was the associate who has been jailed who killed Mr Taylor in two separate attacks, one with a claw hammer and the second with a set of knuckle dusters.

Mr Edhouse testified the associate was angry because Mr Taylor did not want him staying at his house.

Mr Edhouse, right, and Corey Dymock are accused of killing Mr Taylor. ( Supplied: Facebook )

He said the first attack happened after he saw the associate grab a claw hammer and go into Mr Taylor's bedroom.

Mr Edhouse said he followed and as he walked towards Mr Taylor's bedroom he could hear the associate yelling and what sounded like "three consecutive hits".

He said when he went into the bedroom he was "stunned" at what he believed had happened.

Mr Edhouse said he urged the associate to call an ambulance but the man refused, saying he did not want to go to jail.

He told the court they then went outside but seconds later they returned to the bedroom and the associate attacked Mr Taylor with a set of knuckle dusters.

"This was animal-like, he looped out on him," Mr Edhouse told the court.

"Everything was pretty intense, it was a surreal feeling. Half of me wanted to leave, half of me wanted to help Alan.

"He didn't deserve it the first time, let alone the second time. I was too weak to do anything."

The court has heard the associate pleaded guilty to a murder charge and received a reduced sentence in return for testifying at the trial.

Under cross-examination from state prosecutor Justin Whalley, Mr Edhouse said he had "no ill will" towards Mr Taylor, but while he "got along with him", he "wouldn't call him a friend".

Mr Edhouse said his relationship with Ms Attwood was "not kept a secret" from Mr Taylor, who he described as being a "submissive" to Ms Attwood's "dominant".

"They had a pretty unique relationship," he said.

"Alan really didn't have much of a say in what happened. That was my perception."

Neither Ms Attwood nor Mr Dymock elected to give evidence at the trial.