Hamas political chief Ismail Haniyeh was assassinated by a bomb smuggled months ago into the Tehran guesthouse where he was staying, according to a New York Times report.
Investigations found that the bomb was detonated remotely in his room, killing the Hamas leader and his bodyguard instantly.
The explosion shattered some windows and caused the partial collapse of an exterior wall. It appeared to do minimal damage beyond the building itself, dismissing speculation that Israel relied on a missile strike.
The security lapse at the Neshat compound, heavily guarded by Islamic Revolutionary Guards Corps, exposes a catastrophic intelligence failure in Iran.