The House by the Cemetery

A woman (Daniela Doria) is in an abandoned house looking for her boyfriend. After she discovers his body stabbed with scissors, she is stabbed in the head with a French knife, and her body is dragged through a cellar door.
In New York City, Bob (Giovanni Frezzi) and his parents, Norman and Lucy Boyle (Paolo Malco and Catriona MacColl), are moving. Norman's ex-colleague, Dr. Peterson, who murdered his mistress before committing suicide, was the previous owner. The Boyles are to stay there, whilst Norman researches old houses. As his mother packs, Bob looks at a photograph of a house and notices a girl in it. In New Whitby, Boston, Bob waits in his parents' car while they collect keys. The girl from the photograph appears across the street. The girl, Mae (Silvia Collatina), whom only Bob can see, warns him to stay away. In the real estate office, Mrs. Gittelson (Dagmar Lassander) is annoyed when her colleague hands the couple "the Freudstein" keys. She insists it is called "Oak Mansion". Gittelson promises to find a babysitter.
Oak Mansion is in a poor state of repair. The cellar door is locked and nailed shut. A woman arrives and introduces herself as Ann, the babysitter (Ania Pieroni). That night, Norman hears noises and finds Ann unblocking the cellar door. The next day, Norman goes to the library to peruse Peterson's materials. The chief librarian, Mr Wheatley (Carlo De Mejo), appears to recognize him but Norman claims he is mistaken. The assistant librarian, Daniel Douglas (Giampaolo Saccarola), then informs Norman that Peterson conducted private research at the house. He studied records of area disappearances and other demographic data.
Mae shows Bob a tombstone on the grounds marked "Mary Freudstein" and says she is not really buried there. Indoors, Lucy finds the tombstone of "Jacob Tess Freudstein". When Norman returns, he reassures her that some old houses have indoor tombs, because of the hard wintry ground. Norman opens the cellar door and walks down the stairs only be attacked by a bat, which he stabs. Spooked, the family drives down to the estate office and demands to be re-housed, but are told it will be few more days before they can move. While the Boyles are at hospital to treat Norman's injuries from the bat, Gittelson arrives at the house to tell them of a new property. Letting herself in, she stands by the Freudstein tombstone, which cracks apart, pinning her ankle. A figure emerges, stabs her in the neck with a fireplace poker, and drags her into the cellar.
The next morning, Lucy finds Ann cleaning a bloodstain on the kitchen floor. Ann eludes Lucy's questions about the stain. Over coffee, Norman tells Lucy that he's discovered that Freudstein was a Victorian surgeon who conducted illegal experiments. Norman must travel to New York to research Freudstein. On the way, Norman drops by the library and finds a cassette of Peterson, which explains Freudstein killed his family. Ann goes to the cellar looking for Bob, but Freudstein decapitates her after slashing her throat. Bob sees Ann's head, and exits screaming. Lucy refuses to believe Bob's tale about Ann. That evening, Bob returns to the cellar looking for Ann. Lucy hears Bob's cries and tries to open the cellar door. When she cannot open the door, Norman returns and attacks it with an hatchet. The rotting hands of Freudstein (Giovanni De Nava) appear and restrain Bob. Norman cuts the monster's hand, and he staggers away, holding Bob.
The cellar contains mutilated bodies, surgical equipment and a slab. Freudstein is a living corpse with rotting flesh. Norman tells Lucy the 150-year-old Freudstein lives by using his victims' parts to regenerate blood cells. Norman attacks Freudstein, but the ghoul twists the hatchet away. He grabs a dagger off a tray and stabs Freudstein. Freudstein picks up Norman and rips his throat out. Lucy and Bob climb a ladder leading to the cracked tombstone. Lucy strains to shift the stone, but Freudstein grabs her. Freudstein kills Lucy by ramming her head into the concrete floor. As Freudstein advances up the ladder, Bob strains to escape. Suddenly, Bob is yanked upwards and finds Mae. With Mae is her mother, Mary Freudstein (Teresa Rossi Passante), who urges them to leave. Freudstein leads Mae and Bob down the wintry grove into a netherworld of ghosts and sadness.

Question: Who murdered his mistress and committed suicide?
Answer: Dr. Peterson