It's been said to have happened that way but there are theories ranging from his driver/bodyguard Butch Blasi (Who IMP was the one who did it) to Anthony Spilotro (Implicated by capo Sal Bastone) and even on orders from Santo Trafficante. Butch Blasi was supposedly seen by agents earlier in the day then left and came back in a different vehicle but managed to avoid detection coming into and leaving the house. Spilotro was rumored to know the house inside and out as well though.