A police lieutenant in Montgomery County shot and killed his 17-year-old son in self-defense yesterday after the teen lunged at him with a hunting knife, according to county prosecutors.

Police had responded to the family's Towamencin Township home twice recently to subdue Stephen Schmitz, according to Montgomery County District Attorney Risa Vetri Ferman, and the teen was released from a behavioral-health treatment center Tuesday after nearly a two-week stay.

Lt. Eric Schmitz shot Stephen in the chest at their home after the teen tried to attack him with a 10-inch knife with a 5-inch fixed blade, prosecutors said.

Schmitz, a lieutenant of administration with the Hatfield Township Police Department, suffered minor injuries and was cooperative with county police, who are investigating the incident, according to reports.

Police were sent to the home on Oxford Road on April 30 after the boy became enraged and threatened to hurt himself, authorities said.

On May 26, police were again dispatched to the house after Stephen threatened to kill himself, according to the district attorney.

Schmitz subdued his son in that incident, and the boy was involuntarily committed to the Horsham Clinic in Ambler the same day.

By last night, hundreds of friends had joined an online memorial for the teen, who was a junior at North Penn High School in Lansdale.

"Stephen you were such an amazing person," one friend wrote on the page. "Your smile and laugh always lightened the mood and your presence could brighten everybody's day. I'll cherish the times in chorus and when we used to have neighborhood get-togethers. I'll miss and love you forever."