Andrew Hodson, son of slain police informer Terence Hodson, has called in sick to the Victorian inquest into his parents' deaths for the second time this week, delaying his cross-examination.
The inquest was due to finish today and Mr Hodson was scheduled to be cross-examined over his knowledge of the 2004 murder of his father and mother, Christine.
Coroner Ian Gray described Mr Hodson as a vital witness who was required to assist him in "getting to the bottom" of the double murder.
Mr Hodson's lawyer told the inquest he was in hospital and may require surgery, making it impossible for him to give evidence.
He said his client may be unwell for some time.
Earlier this week, a former Petra Taskforce detective, Cameron Davey, told the inquest that Mr Hodson was once considered a suspect in murder of his parents.
The couple was shot dead execution-style in the back room of their Kew home in 2004.Andrew Hodson knew Tony Mokbel: Detective
Mr Davey said police still suspected Mr Hodson of releasing of sensitive information on the layout of his parents' home and its security system.
He said Mr Hodson was a known associate of drugs boss Tony Mokbel and may have given the information out "inadvertently" to the killers, or Mokbel himself.
The inquest heard Mr Hodson had once failed a lie detector test on the subject.
Mr Hodson appeared briefly in court last week to hear his police statements read out.
Mr Gray said he would allow Mr Hodson to give evidence via video link from his now home state of Queensland, if he preferred to return there after leaving hospital.
"I want it to be very clear to him," Mr Gray said.
"He's a witness now and sworn up... he's required to give evidence in this case.
"The message to him is it will assist me and I want him to give evidence."
Mr Gray also invited the Hodson's daughters, Mandy and Nicole, who have been present throughout the inquest, to give evidence or make a statement about their parents to the court.
He said such information may "shed light" on the case.Mokbel says Dale 'owed him big time': witness
Terence Hodson had been due to give evidence against former detective Paul Dale over a drugs burglary, at the time he was killed.
Mr Dale and career criminal Rodney Collins were once charged over the murders, but the charges were dropped when underworld boss Carl Williams was killed in Barwon Prison.
They have always denied involvement and were excused from giving evidence at the inquest.
Yesterday, a witness who could not be identified, told the inquest that Tony Mokbel had once told him that there were "50,000 reasons" that Mr Dale "owed him big time".
Witness M said that he interpreted Mokbel's words to mean he had payed Rodney Collins to have the Hodsons killed, on behalf of Mr Dale.
The witness also claimed Mokbel told him, Carl Williams "paid the rest".
The inquest will resume on August 15.