An 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 a violent attack at the centre in Harmondsworth, West Drayton, Greater London, and was pronounced dead.
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 told the court 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 the case 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.
The defendant, who was helped by a Kurdish translator, was remanded in custody.
The victim's family sat in court throughout the short hearing.