A man accused of murdering his flatmate has told a jury the woman died after inhaling nitrous oxide and he was too “panicked” by the risk of criminal charges to seek help.

Yang Zhao, 30, on Wednesday took the stand in his own defence at trial after pleading not guilty to the murder of Qiong Yan, 29, in September 2020 at their inner-Brisbane apartment.

He has instead pleaded guilty to interfering with Yan’s corpse, which was found concealed in a large tool box on their unit’s balcony about 10 months after her alleged murder.

The Supreme Court jury previously saw two police interview videos of Zhao telling detectives he killed Yan by beating her on the head with a metal cream-whipping bottle then strangling her.

Defence barrister Andrew Hoare told the jury that Zhao, during his evidence, would admit he used Yan’s phone after her death and impersonated her in text messages to her mother to obtain money.

“He wanted the death penalty … he had immense shame and guilt. He then maintained the lie to police in order to be punished for his shameful and despicable conduct,” Hoare said.

Zhao on Wednesday told the jury he had been drinking whiskey, and he and Yan had inhaled nitrous oxide between 9pm and 11pm on the night he said she died.

“Every evening we would do the gassing,” Zhao said with the aid of a Mandarin Chinese interpreter.

Yan’s mother was in court to hear Zhao’s evidence after travelling from Shanghai to Brisbane.

Zhao said Yan had passed out on the apartment’s floor at some time after 11pm and he had fallen asleep on a nearby sofa due to being “pretty high”.

The jury heard Zhao woke up and did not want to disturb Yan.

He said he took his dog for a 10-minute walk before returning at 1am.

“I noticed she was in the same position as when she left. When I got closer I could see her body wasn’t moving and she wasn’t breathing,” he said.

The jury heard Zhao always bought the nitrous oxide for himself and Yan, buying two to three boxes at a time that each contained 60 small gas bulbs.

“I was panicked. I was worried that I would get in trouble,” Zhao said.

“After I saw her like that I thought nothing I could do would make much of a difference. I went to her room to get her quilt cover and put that on her.”

The jury last week heard evidence from forensic pathologist Beng Ong, who performed an autopsy on Yan.

“A cause of death cannot be ascertained due to the decomposed state of remains,” he said.

Ong testified that damage to Yan’s forehead and neck cartilage could have been caused either by blunt force trauma and strangulation respectively, or by the decomposition process.