Media playback is unsupported on your device Media caption Two men who were in prison with Dr Khan say he was killed because he was witness to the brutality that prisoners suffered

A UK doctor found dead in prison in Syria was killed because he kept a diary of the brutality he witnessed in jail, a former inmate has told the BBC.

Dr Abbas Khan was working in a field hospital in a rebel-controlled part of Syria when he was arrested in 2012.

Syrian officials said Dr Khan's death in custody more than a year later was suicide, but his family dispute this.

Two former inmates, speaking to the BBC in Syria, claimed Dr Khan was in a positive frame of mind.

On Monday a pre-inquest hearing revealed that a psychiatrist would investigate Dr Khan's mental state.

'Brutality'

One of the men, who wanted to remain anonymous for fear of reprisals, claimed the 32-year-old surgeon was killed because he had kept a diary about what he had seen.

He said: "He used to tell us about how they used to beat him and hang him up by his hands.

"I remember he had lots of dark bruises.

"He saw people dying in front of him. Abbas saw the brutality. They killed him for the things Abbas saw."

Dr Khan, an orthopaedic surgeon from London and a father-of-two, crossed into Syria from Turkey without a visa and was captured in Aleppo, where he had volunteered to help treat casualties.

He died last year after being initially arrested in November 2012.

Syrian authorities say he was found hanged in his cell, but the UK Foreign Office has said he was "in effect murdered".

His family also believe he was killed by his captors.

Dr Khan's body was flown back to the UK less than a week after his death and a post-mortem was carried out.

The inquest is listed for 13 October and is due to last for three weeks.