Prosecutors in Kassel accuse the 32-year-old of creeping up behind his father in the cowshed and beating him to death before strangling his mother in her sleep four years later.
The defendant claims he is innocent and that his father was killed after being kicked by a cow. He is accused of killing his parents to get his hands on the family farm.
He has however admitted sawing up the body of his 73-year-old neighbour, who died on his farm in February 2005, freezing the pieces and feeding some of them to his pigs. He said he wanted to continue collecting his neighbour's pension.
Prosecutors said the accused needed the money to pay off some of the farm's €300,000 ($480,000) in debt.