Police say a man has been arrested for stabbing his grandfather to death inside a Shirley home.

Police say John Pilgrim, 80, was at his home on Hounslow Road, when his grandson Christopher Clarke stabbed him to death at 7:45 p.m.

Clarke then fled the scene on foot, according to police.

Pilgrim was pronounced dead at the scene by a physician assistant from the Office of the Suffolk County Medical Examiner.

Kim says Pilgrim was her uncle, and she was the one who found him dead in his room.

"He is laying on his bed, the covers is over him, I'm screaming his name and he's not moving," Kim says. "I go up to him and see the blood on the wall, and I pull the cover back and he's dead."

Detectives say Clarke was located and arrested at the LIRR station in Shirley at 9:41 p.m. Monday.

Police have charged Clarke, 34, of Brooklyn, with murder in the second degree. He could face life behind bars if convicted.

Clarke was arraigned Tuesday in Central Islip. News 12 saw him before his court appearance where he was smiling and proclaiming to be a higher power.

"All I know is I love the most high, and I am Jesus Christ," Clarke said.

Clarke's sister, Erica Quill, of Mastic Beach, spoke exclusively to News 12 and was shaken and upset. Quill says her brother has had mental health issues and that she's grateful he's in a safe place now.

"Dealing with the mental issue, he did call him a demon, so I feel like in his mind he felt he had to make sacrifices," Quill says.

Quill said her older brother had threatened to harm their grandfather before, but she was stunned by what happened.

Quill says Clarke had previously threatened their mother, who he believed was a demon, and held a knife to her while she had Quill's baby in her arms.