A coroner has urged police to take further steps to investigate the death of a profoundly disabled man at a nursing home in Northern Ireland.
Joe McCrisken said the cause of Seamus McCollum's sudden demise was undetermined.
He was unable to find if the death was accidental or deliberate after marks were found on the neck of the wheel chair-bound cerebral palsy sufferer at the Co Antrim home in September 2011.
Mr McCrisken said it was the most difficult case he had had to deal with as a coroner or previously as a barrister.
"The death of Seamus McCollum remains shrouded in mystery.
"I believe that police should continue to investigate Seamus McCollum's death, although I cannot compel them to do so."
He said he shared the family's frustration at the imperfections of the inquest process.
"It is my view and it would benefit everyone if the police did take some further action here."
The cause of the 56-year-old's death was undetermined by two pathologists but strangulation could not be ruled out.
The coroner said he died between 3-4am and was not breathing when a care assistant entered his room and raised the alarm at 6am on September 12.
Mr McCrisken could only find that the neck injuries happened some time between 11pm the night before and 6am the day he was found dead.
He said a flat triangular object like a necklace or belt was the likely reason for the marks.
Mr McCrisken found police did not search the room thoroughly following his death and any implement responsible may have been removed accidentally or deliberately.
The coroner's court in Belfast was told a full murder investigation was only launched several months after the death when post-mortem results were confirmed.
Two trainee detectives had initially attended the scene but senior colleagues decided to pass the matter to ordinary police without actually entering the room where the death happened, witnesses told the inquest.
Mr McCrisken told Detective Constable Beverly Gannon: "A cynic would say it would be in the police's interest to get a natural death for this because it would excuse you dropping the ball in 2011."
He added: "Some would say I am a cynic."
Ms Gannon said in any investigation police had to keep an open mind and they had to be guided by experts.
A doctor had expressed concern about the injury.
A forensic expert at the scene had told her Mr McCollum's long nails may have caused it but said it was up to the post mortem to determine the cause of death.
The keen Manchester United football club supporter spent most of his life in care, from age five.
He had been in the Maine home in Randalstown for almost a decade.
He was fed through a tube as he had difficulties swallowing and lifted in and out of bed using a hoist.
The coroner said he probably died from a heart attack brought on by compression of his neck.
He regretted that, based on the current evidence, he was unable to answer the family's questions.
"An inquest can be an imperfect process and frustrating for the family and on this occasion I want the family to know I share that."
He added: "It seems to me that there are some further steps that could be taken."
A PSNI statement said: "Seamus McCollum's death in September 2011 remains a murder investigation."