pentito

Etymology
Borrowed from.

Noun

 * 1) A criminal who cooperates with police or government authorities and testifies against or provides harmful information on fellow criminals; a turncoat or informant, usually a former Mafioso.

Noun

 * 1) one who repents
 * 2)  a criminal who cooperates with police or government authorities and testifies against or provides harmful information on fellow criminals; a turncoat or informant. Used mostly in reference to ex-Mafiosi