A mentally ill Iraqi man has admitted beating to death a fellow detainee at an immigration facility.
Zana Yusif, 32, killed frail Bangladeshi national Tarek Chowdhury in a cell at Colnbrook Immigration Removal Centre on December 1 last year.
Mr Chowdhury, 64, was taken to hospital following the violent attack at the centre in Harmondsworth, West Drayton, Greater London, and was pronounced dead.
Investigations revealed that Mr Chowdhury had gone into cell five which contained two other people, followed a few minutes later by Yusif.
The defendant, who was not wearing any trousers, asked for a lighter then grabbed Mr Chowdhury, shook him and repeatedly punched him in the head, police said.
A short time later, Yusif and one of the other detainees left the cell and the remaining detainee emerged looking "panicked".
He flagged down a member of staff who discovered Mr Chowdhury fatally hurt, Scotland Yard said.
Yusif, whose hands were reddened and injured, was arrested on suspicion of murder and charged the following day.
Kurdish-speaking Yusif appeared at the Old Bailey and pleaded not guilty to murder, but guilty to manslaughter by diminished responsibility.
Prosecutor Jake Hallam QC said the Crown accepted the plea in light of two psychiatric reports which concluded that Yusif was suffering from an "abnormality of the mind" at the time of the killing.
He told the court that both Yusif and the victim were resident at Colnbrook, awaiting deportation.
He said Yusif had a "psychiatric history" which was noted at different times when he had served "shortish sentences" in custody.
Judge Richard Marks QC adjourned sentencing until June 21 pending a further report.
Colnbrook detains people subject to immigration control and has the capacity to hold up to 396 men and 27 women.
The centre, adjacent to Heathrow Airport, is operated by Mitie Care and Custody which won the contract to run the centre in 2014 after Serco ran it from its opening in 2004.
Detective Inspector James Stevenson, of Scotland Yard, said: "This was a vicious unprovoked attack on Mr Chowdhury that ultimately cost him his life.
"I am pleased that Yusif has finally taken responsibility for his actions."