Two staff have been suspended after a prisoner was found hanged in his cell.
Michael Bailey, 23, was serving four years for drugs offences at the privately-run category-B prison HMP Rye Hill, Warwickshire.
A spokesman for Northamptonshire Police, who are investigating, said: "Two members of prison staff have been suspended pending an internal inquiry."
Michael Bailey had been at Rye Hill since December. It is not known whether he was classed as vulnerable.
Rye Hill is a private finance initiative (PFI) prison which opened in January 2001.
It holds 660 adult male prisoners, including 150 vulnerable inmates in a purpose-built unit.