Open Grave

A wounded and dirty man awakes in a pit full of cadavers during the night and a woman throws a rope to him. He leaves the pit and finds a house, where there are five persons, two women and three men, four of them amnestic. The one who saved him is mute and the other four persons find documents with their names: Lukas, Nathan, Sharon and Michael. In the morning, they walk around the house and find several corpses and they have glimpses of memory. The question is, who committed the crime spree?