WATERTOWN, Conn. (AP) — Two teenage siblings and their mother’s boyfriend died in what appears to be a murder-suicide when an argument over smoking in a Connecticut home got out of hand, police said Wednesday.

Officers responded to the Watertown home at about 10 p.m. Tuesday after a woman called 911 to report the shooting, police said.

Sterling Jette, 16, and Della Jette, 15, were taken to Waterbury Hospital where they were pronounced dead.

Police also found Paul Ferguson, 42, dead at the scene of an apparently self-inflicted gunshot wound.

Chief John Gavallas says both teens were shot in the chest.

Ferguson had moved into the home two weeks ago and as a convicted felon, was not allowed to have a gun, police said.

The teens’ mother was not hurt and is cooperating with the investigation.

Both teens were students at Kaynor Technical Institute in Waterbury.

“These domestic incidents can turn violent so quickly,” Gavallas said. “And this mother is completely distraught.”

Police say Della returned from a school field trip and started loudly discussing with her mother about Ferguson smoking cigarettes in the house.  Ferguson, who was downstairs with Sterling, told her to quiet down and not speak to her mother that way.  Police say he went to the bedroom, came back with a Glock handgun that was kept in a safe and shot Sterling in the leg when he tried to intercede.  Police say the girl was found on the deck.  The boy was found between the kitchen and living room.