Police were called to the house by the couple's son who said that his parents, Franz and Heidi R., 60 and 54, were missing and that there was a "large amount of blood in the stairway of the house," a police spokesman said on Monday.
Shortly afterwards officers found two bodies in the garden of the house in Notzing, near Ingolstadt. An autopsy confirmed that the couple were killed by multiple stab wounds.
They said the 21-year-old man gave himself up while officers were at the house, and confessed. Police later found several knives in the young man's flat, though they are not sure which, if any, was the murder weapon.
The man is thought to have behaved violently towards both his own family, as well as his girlfriend's, in the past. “The background to the case remains unclear,” said police spokesman Peter Grießer.
Detectives have sealed off the house and the street nearby, where it seems the bodies were first buried before being dug up and reburied in the garden.
Police suspect that the daughter may have been involved in her parents' deaths, though it remains unclear in what way.
According to a report in Bild newspaper that cites anonymous police sources, she is not thought to have been directly involved in their killing, but may have helped hide the bodies. She was reportedly in the house, where she lives, when her brother came in and phoned the police.