The 51-year-old man will spend the rest of his life in prison in an unusually harsh ruling for Germany, where jail terms for murder are often limited to 15 years. But the Munich court said the severity of what he did meant he should never be freed.
The man, identified only as Thomas S., killed eight-year-old Chiara and her 11-year-old sister Sharon as they were in their home in the small Bavarian village of Krailling last March.
Their mother found their bodies when she returned home late from the local pub with her partner.
The court heard that Thomas S. had built up large debts while building a house, and had originally planned to kill his sister and her two children to make himself sole heir to the family fortune. It was only by chance that Thomas S. did not also kill his sister as planned, the court heard.
And although Thomas S. had continually denied the murder, the judge ruled that the possibility of someone else being responsible could be ruled out, thanks to his DNA being found on the rope, knife and training weight used to kill the girls.
Shortly before the trial ended, Thomas S. set out a conspiracy theory in which he said he had been set up, claiming that detectives had left blood traces at the scene of the murder.
The public prosecutor said these were fantasies, and that his accusations were in danger of putting him in line for further prosecution.
“One would have to laugh if it were not so sad,” said prosecutor Florian Gliwitzky.