Gene Gibson, 25, who is from the remote desert community of Kiwirrkurra and speaks the Pintupi dialect, is serving seven-and a-half years behind bars for fatally striking 21-year-old Josh Warneke from behind as he walked home from a night out in Broome in 2010.
A series of flawed police interviews more than two years later were deemed inadmissible, forcing prosecutors to drop a murder charge and accept Gibson's guilty plea to manslaughter.
But Gibson claims he gave a false confession because his lawyer said he'd get a longer jail term if he pleaded not guilty.
Gibson's conviction is being appealed, on the basis he suffered a miscarriage of justice, because he did not have the cognitive ability or language skills to understand what was happening.
Through an interpreter, he told the WA Court of Appeal earlier this week that he'd made a false confession.
Gibson claimed he wanted to plead not guilty, but his lawyer, Dominic Brunello, told him he'd get a longer sentence than if he pleaded guilty.
Mr Brunello testified on Wednesday, denying he'd made the comment to Gibson.
He said he was aware his client spoke limited English, but had at times not been able to get a translator.
"When I spoke to him in English, I tried to keep it as plain and as simple, and as short, as possible," the lawyer told the court.
Mr Brunello also said the Director of Public Prosecutions had indicated just weeks away from trial that the state's preparedness to accept a plea to manslaughter was finite, with words to the effect of "we'll do this now, but not later".
"I felt I had to do things expeditiously," he said.
Three days after he met his client without an interpreter, Mr Brunello flagged the plea offer with the judge's associate, who advised five days later that the judge had raised concerns about whether he had taken instructions from Gibson without an interpreter.
Mr Brunello said that had troubled him too, and he was relieved when the court intervened and the matter was adjourned.
Gibson entered his plea after meeting Mr Brunello with the help of an interpreter, Robert Nanala, who was flown to Perth from Halls Creek.
Mr Nanala testified earlier this week that Mr Brunello told his client: "If you do not plead guilty, you'll be going for a long, long time."
Mr Brunello told the court a doctor had assessed Gibson as being fit for trial, so he was not aware that he had any impairments, aside from some hearing issues.