One-legged man beats mother to death with crutch.

Jesus.

A one-legged Queens man beat his 80-year-old mother to death with a crutch Friday - then called the cops and confessed.

"I just killed my mother and I don't know why," Sergeui Mamontov said, according to a police source.

When cops arrived, they discovered that Mamontov had also tried to castrate himself, telling the officers he was "trying to remove the evil," a police source said.

Mamontov, who has a history of mental illness and tried to commit suicide before, was taken to Bellevue Hospital, the source said.