A second inmate has been arrested by detectives investigating the death of a prisoner at a Buckinghamshire prison.
Prisoner Robert Coello, from Berkshire, who was serving life for raping a child died on Sunday after he was discovered in his cell at Grendon Prison.
A fellow 28-year-old inmate was arrested on suspicion of assisting an offender and later bailed.
Police had previously arrested a 25-year-old man on suspicion of murder, who was then bailed back to the prison.
Found by staff
Grendon Prison houses up to 235 inmates in Category B secure conditions with the six wings operating as therapeutic communities.
Prisoners must be committed to staying drug-free while in therapy.
Coello, 44, from Whitley, was found by staff in his cell in the prison's G wing at 1540 BST on Sunday.
He was taken to Stoke Mandeville hospital but later died. A post-mortem examination is expected take place later.
Coello was jailed in 2006 after admitting four counts of rape and other offences, and told he must serve a minimum of seven years.