77-year-old James Griffin, of Chicago, Illinois, was watching television with his son, 48-year-old Michael Griffin. The two fell asleep but at some point Michael woke up and left the apartment. When he came back in James thought Michael was a burglar and shot and killed him.
Police found Michael, who was shot once in the head, dead in his father's home.
James Griffin was a retired police officer. He had served for 42 years as a homicide detective on Chicago's West Side. He retired in 1998.
Michael had recently been evicted from his apartment and had moved in with his father and one of his brothers.
His brother, Stephen, told reporters that his father's senses "aren't as sharp as they used to be," but added that he is in good physical health.
No charges have been announced by police.