Lieutenant Eric Schmitz was being treated for his injuries in hospital last night after allegedly killing the teenager on the front lawn of their home in Towamencin Township, Pennsylvania.
Prosecutors say his son, Stephen Schmitz, had only been released from a psychiatric clinic the day before.
He had been admitted for treatment two weeks before, when he threatened to kill himself.
According to police, Lieutenant Schmitz shot his son in self-defence after Stephen ran at him with a five-inch hunting knife at around 3pm on Wednesday.
Video footage taken soon after the incident shows officers speaking to the lieutenant, who looks visibly shaken, on the front porch of his home.
Neighbours in the quiet, upscale district said they were stunned by the shooting.
Lieutenant Schmitz, who works for the Hatfield Township police department, was later taken to hospital for treatment where officials said he was being questioned.
They also revealed police had been called to the the house twice before, first in April, when Stephen, a junior at North Penn High School, became 'enraged' and threatened to harm himself.
In a press release, Montgomery County District Attorney Risa Vetri Ferman said tensions seemed to have eased in the family, but then police were called again on May 29 after Stephen threatened to kill himself.
He was involuntarily committed to the nearby Horsham Clinic for two weeks, and was released on Tuesday, the day before he died.
By this morning, a memorial page set up for the popular 17-year-old on Facebook had attracted more than 1,800 members.
Stephen was described as an 'actor and director', and friends also paid tribute to his lacrosse skills. Read More