The parents of a Kent man are trying to piece together seven missing hours which led to their son ending up in a coma with little chance of recovery.
Denby Collins, 38, was arrested on suspicion of burglary at a house in Gillingham on 15 December, then taken to hospital in a serious condition.
"We just really need to understand what has gone on," said his father Peter.
Kent Police said it was investigating how Mr Collins came to be in the house.
His parents have instructed lawyers because they are unhappy with the information they have received from the force.
They fear police failed to investigate adequately what happened between 20:00 GMT on 14 December when they spoke to their son on the phone and the early hours of the next day, when he was arrested.
Handcuffed by police
Lawyer Daniel Machover said he had established that Kent Police was investigating an assault on Mr Collins.
"Denby was handcuffed by police officers when they were called to private premises regarding an alleged burglary," said Mr Machover.
"We understand that on being handcuffed it was realised that (he) was unconscious and seriously unwell.
"A police medic at the scene used a defibrillator to revive Denby Collins, who otherwise would have died."
Mr Collins has been in a coma ever since.
"It is likely that he is going to be severely handicapped for the rest of his life because of his brain injuries," said his father.
"It is very difficult because we just can't get closure on this.
"It is such a shock when he was a young man in his prime."
Kent Police said in a statement: "A 38-year-old man was arrested on suspicion of burglary and taken to hospital for medical treatment.
"Inquiries are ongoing into the circumstances of how he came to be in the house.
"Detectives are particularly interested in speaking to people who saw Denby Collins between 16:00 GMT on 14 December and 03:15 GMT on 15 December."