POLICE investigating the murder of underworld figure Stephen Cookson, whose head washed up on Rottnest Island on Sunday, are understood to have questioned a man about the gruesome case overnight.

Its understood detectives investigated a man at length over the death of Cookson, 56, but released him without charge, pending further inquiries.

Major Crime Squad detectives are now speaking to two men over the murder.

Police spokeswoman Naomi Smith said the ages of the men were yet to be confirmed and they were assisting with the investigation.

"No charges have been preferred and there is no further information we can release or confirm at this time," she said.

News of a man being questioned last night came as police descended on a home in Perth’s southern suburbs late yesterday.

Forensic police combed through the Ellendale Street home in Golden Bay, about 60km south of Perth.

WA police had earlier confirmed the head washed up on Rottnest Island belonged to the underworld figure, amid reports detectives had also quizzed those who may have dumped his remains.

The remains of Cookson were discovered on the island by an 11-year-old girl on Sunday, who was beachcombing with her family at Porpoise Bay on the southeast of the island.

A long-time member of the seamier side of the racing industry in Victoria and WA, Cookson was convicted in WA in 2000 on one count of being in possession of a quantity of heroin with intent to sell or supply.

He unsuccessfully appealed that conviction all the way to the High Court, where the former law student chose to represent himself.

In 2005, Cookson was fined $5000 for improper conduct by WA racing authorities, namely assaulting a former horse owner Peter Graham, breaking his nose.

That fine was also appealed unsuccessfully.

A self-appointed "equine consultant'', Cookson had been due to appear in WA's District Court tomorrow on a charge of possession of methylamphetamine with intent to sell or supply.

Cookson once claimed to have studied law with former Federal treasurer Peter Costello.

PerthNow was told he boasted of having been a classmate of the former treasurer at Monash University in the 1970s.

Those who knew him said he was extremely intelligent but highly volatile, well known in racing circles in his adopted state of WA and was a huge gambler