After the Dr. arrives and looks around, he's in the living room with Sam and Thomas. Thomas shows him the paper and the doctor says the name and that it is German for nightmare, or something to that effect. He states that it is believed that 'Maron' is a nightmare that attacks women while they sleep. He goes on to say that it is like the Christian form of incubi [sp?], where women are raped in their sleep.
I think this 'presence' felt the doctor was a threat in some way and killed him. The whole room looked ransacked and the ashes were by the living room opening. The doctor had explained that the mother 'contacting' her husband probably encountered a bad one that took over the husbands presence, to get into their lives and their home.