Crown prosecutor Michael Barr in the NSW Supreme Court on Thursday questioned why Alex Dion had thrown his workwear into the same tank he used to hide clothing and other items from murdered man Wachira "Mario" Phetmang.

If the clothing he wore as a tiler was damp, why not wash them instead? Mr Barr asked.

"What do I need them for, I'm going to America," Dion said.

"In America, I never worked as a tiler ... I don't need working wear ... I worked in a restaurant for 13 years."

The 40-year-old has been extradited back to Australia and pleaded not guilty to murdering Mr Phetmang between May 25 and May 27 in 2018.

A truck driver found Mr Phetmang's extensively decomposed body bound and gagged in bushland outside Sydney Olympic Park on June 6.

An autopsy later found the cause of death was likely from at least 27 head injuries causing fractures to his skull.

The US citizen has accused his former flatmate Adib El-Anani of the murder and said he did him a "big favour" by disposing of the body in his car which he then thoroughly cleaned inside.

Mr Phetmang had been dealing the drug ice to Dion for some weeks before he was killed.

Dion had moved in with his "lifelong friend" Mr El-Anani and given work at his tiling business, while waiting for a compensation claim in Melbourne, before the relationship deteriorated.

Four days into giving evidence Dion said the last time he saw Mr Phetmang was with Mr El-Anani at a Hurstville 7-Eleven where Dion and Mr Phetmang were pictured together on CCTV footage.

There is no evidence to suggest Mr El-Anani ever attended the convenience store on the night Mr Phetmang was last seen alive.

The Crown also questioned Dion's story that Mr El-Anani had inflicted the fatal blows on Mr Phetmang, asking if he noticed any blood or sweat on his friend immediately after the incident.

"I was not really concerned if he was sweaty or not," Dion said.

Dion said when he drove to a Belmore apartment Mr El-Anani was waiting in the parking lot with Mr Phetmang and murdered him while he went upstairs.

In an intercepted phone call, Mr El-Anani asks Dion why he left the country and his car "washed inside-outside," with the keys.

"Thank you that you called, thank you, thank you, thank you," Dion responds before the call is ended.

Dion testified the pair had agreed not to speak of the murder over the phone or by text, despite him already implicating his former friend in the crime to a senior constable in Australia.

He earlier stated that he felt stupid for disposing of the body and concealing evidence on a building site he had previously worked on.

Two days after the alleged murder Dion flew to America to be with his wife. He took with him Mr Phetmang's mobile phone and credit cards which he used when possible.

The trial continues.

Australian Associated Press