Wheelchair-user Seamus McCollum, 56, had cerebral palsy and was fed through a tube.
Mr McCollum died at the Maine Nursing Home in Randalstown.
A doctor told a Belfast inquest into his death that marks were found on his face and neck after his death.
Assistant state pathologist Dr Peter Ingram said there were “a considerable number of worrying injuries, principally to the neck or face, for which no satisfactory plausible explanation has been proffered”.
He said: “The possibility of strangulation cannot be excluded. The possibility of smothering needs also to be considered.”
Dr Ingram said it was highly unlikely some of the injuries were sustained during attempts to resuscitate Mr McCollum.
Mr McCollum had spent most of his life in care and had been in the Randalstown home for almost a decade.
He was fed through a peg as he had difficulties swallowing and was lifted in and out of bed using a hoist.
Mr McCollum could not control his head and used a board to communicate. Despite his challenges, he was in good form before his death, his sisters said.
‘No satisfactory explanation’
Irish state pathologist Marie Cassidy was asked to examine post-mortem findings. She said no satisfactory explanation had been provided for some marks.
There were deep bruises to the neck but no trauma to the skeleton and the cause of death was undetermined.
Ms Cassidy said: “It cannot be excluded that the injuries were caused by a third party.”
Staff nurse Mary Harraghy, who carried out CPR, did not notice any marks on him bar a blemish on his collar bone before she handed him over to paramedics.
She believed elastic from the oxygen mask could have caused the damage when he was moved from the bed to the floor by the emergency team.
Another possibility coroner Joe McCrisken is investigating is whether Mr McCollum fell from his bed.
A fit could be another explanation, Mr McCrisken added.
Claire Thompson was one of the last people to see him alive and in a statement she said she noticed yellow marks on his neck after she returned from calling an ambulance because he had became poorly.
She said: “They shocked me and made me feel uneasy.”
When asked about this on Monday she was unable to remember many of the details.
Other staff said they had not noticed any bruising on his neck before his death and his sisters Molly Gilbert and Bernadette McFall had no complaints about his care up to that point.
Source: BBC News – Northern Ireland