Warwick Toohey, Jake Fairest and Georgia Fields have all pleaded not guilty to murdering Mr Toohey's former housemate, Robert Wright, in January 2015.

The three profoundly deaf and intellectually disabled defendants appeared before the Supreme Court of Victoria on Tuesday for the first day of their special hearing before Justice Jane Dixon. Juries had previously found the trio unfit to stand trial.

Prosecutors played CCTV footage of the trio entering the lobby of the Ringwood building on January 15, 2015 and talking to each other as they waited for a lift to go up to Mr Toohey's apartment.

Prosecutor Christopher Dane, QC, said an interpreter would give evidence that the discussion focused on whether the victim should be strangled or fall to his death.

Mr Fairest, he said, is shown saying "Can strangle neck area, what do you think?"

Ms Fields replies: "I think falling is better."

Mr Toohey signs to Mr Fairest: "Strangle risky."

Ms Fields then signs: "Fall good, fall good."

Mr Toohey signs to Mr Fairest: "You first go in grab,  you say 'hello, how are you', grab and push forward."

The court heard that Mr Wright had suffered cardiac arrest after falling from the second-storey balcony, and later died in hospital from head injuries.

Mr Dane said that the two men had lifted and forced Mr Wright over his balcony, while Ms Fields watched on, though all three had planned his murder together. The trio had given police a number of versions of what happened that night, blaming each other for pushing Mr Wright over the balcony.

Mr Fairest initially told police there had been a scuffle between Mr Toohey and the victim, the court heard. While Mr Toohey pushed him off the balcony, Mr Fairest said he tried to grab the victim, but failed to hold on.

Mr Toohey, who is pleading not guilty by reason of mental impairment, told police that Mr Fairest had lifted the victim over the balcony, and that he had tried to save him but could not, the court heard.

Ms Fields initially indicated to police using a notebook that Mr Wright had jumped off the balcony by himself, Mr Dane said. She later told them that her boyfriend had gotten angry with the victim and pushed him off the balcony.

Ms Fields also told them that the trio had made a plan to kill Mr Wright. Mr Toohey and Mr Fairest had picked him up, but she said that all three were to blame for his death.

Peter Kilduff, for Ms Fields, said this was a small portion of his client's police interview. "The rest of what is said... may become an issue of what her state of mind was regarding what took place that night," he said.

Mr Dane said the court would hear evidence from neighbours, sign language interpreters and people familiar with the relationship between the defendants and the victim.

The jury will decide whether the trio were criminally responsible or not guilty of murder.

The special hearing continues.