The 25-year-old man, whose name was not released, was arrested at the prison in Milton Keynes, Bucks, after guards noticed he seemed nervous as he went through security screening and asked him to remove his leg, The Sun reported Monday, noting the prison houses terrorists, rapists and killers.

Prison officials said they assumed the man was trying to smuggle the canister to a prisoner to be used in an escape attempt or in a feud between inmates, the Sun reported.