A prisoner of Tihar jail stabbed another inmate to death allegedly to avenge the rape of his sister six years ago, police said on Tuesday. On Monday, 21-year-old Zakir stabbed Mohammad Mehtab (27), a resident of Nizamuddin, inside Tihar jail number 8/9. Mehtab was stabbed multiple times, including on his stomach and neck, by a sharp metal object by Zakir at around 6 am, police.