Harry Bosomworth, 70, attacked fellow patients Ken Godward, 76, and Roger Lamb, 79, with a walking stick after being taken off his anti-psychotic medication while being treated for cancer at St James’ Hospital in Leeds in 2015.
The deaths only came to light earlier this year when an independent report into the incident, commissioned by hospital bosses, was leaked.
The trust which runs the hospital has apologised to the families involved, saying it had “let these patients down”, and that it had since made significant improvements to the way it cared for patients with mental health needs.
Inquests into the two deaths have been opened but cannot resume until NHS England has finished its internal investigation process and completed its final review.
Coroners had given NHS England a deadline of May 1 to submit its final report, but the body has now had to ask for an extension and has been given a further 21 days.
Senior coroner Kevin McLoughlin said: “After granting the requested extension I fully expect to have the report by 21 May.
“At that point I will review the file in its entirety and identify a court date to suit the availability of the witnesses who will be required to give evidence in person.”
A spokesman for NHS England said: “Independent investigations require close working with the families and organisations. Given the complexities and sensitivities, timescales cannot always be accurately predicted at the outset but any revisions are made in consultation with all those involved.”
West Yorkshire Police has already said it had carried out a detailed investigation at the time and found “no criminal culpability on the part of the hospital”.
Mr Bosomworth, who had paranoid schizophrenia, died of cancer in June 2015.
His stepdaughter, Rita Martin, told The Yorkshire Post in March that he too was a victim, having suffered “mental torture” after being taken off his medication.
She described how she had repeatedly warned medical staff that Mr Bosomworth was dangerous if he wasn’t taking the anti-psychotic drug Olanzapine.
Yesterday, Ms Martin said while in some respects the delay to the inquest process was frustrating, there had been a benefit in that it had allowed her the time to meet the families of Mr Godward and Mr Lamb last week.
She said: “It went very well. It was quite emotional for all of us.”