It happened around 7:45 p.m. Monday, June 13 in Shirley.
John Pilgrim, age 80, was at his residence, located at 134 Hounslow Road, when his grandson, 34-year-old Christopher Clarke, stabbed him to death, Suffolk County Police said.
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.
Following an investigation, Clarke was located and arrested at the Long Island Railroad Station in Shirley at around 9:40 p.m., police said.
Homicide Squad detectives charged Clarke, of Brooklyn, with second-degree murder.
He is being held at the Sixth Precinct and is scheduled to be arraigned at First District Court in Central Islip on Tuesday, June 14.
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