(WATERTOWN, Conn.) — A dispute between a Connecticut teenager and her mother’s boyfriend over smoking ended in tragedy, after the man shot and killed the girl and her brother, before turning the gun on himself.Police were called to the Watertown, Conn., home of Danielle Jette around 9:45 p.m. on Tuesday. Jette had called 911 saying that her boyfriend had shot her son and daughter.Approximately 10 officers responded to the call and found Della Jette, 15 and Sterling Jette Jr., 16 at the home suffering from gunshot wounds to the chest. Della was on the property’s back deck and Sterling was found between the kitchen and living room.They were given emergency medical care at the scene, before being taken to a local hospital with life-threatening injuries. Both died shortly after arriving at hospital, police said.The suspected shooter, identified as Paul W. Ferguson, 42, was also found at the property with a suspected self-inflicted gunshot wound. He was pronounced dead at the scene.Ferguson was Danielle Jette’s boyfriend and had moved into the home in November 2019.Jette told authorities that the tragic events started with an argument between her daughter Della and Ferguson over his smoking in the house. The argument escalated and Ferguson armed himself with a Glock handgun that was stored in his bedroom and shot Jette’s son Sterling, who had attempted to intervene in the argument, in the leg.“The mother went downstairs to call 911 when she heard a second gunshot presumably when he shot the daughter on the deck. He came back into the house and shot the son in the chest,” said Chief John Gavallas, Watertown Police Dept.Police said Ferguson was a convicted felon and was restricted from possessing a firearm. He had been charged with sexual assault in a spousal relationship, a charge that was pleaded down to unlawful restraint, of which he was convicted.Police say they do not know who owned the gun used in the shooting.Friends of the teenagers held a memorial Wednesday, and spoke of their devastation at the deaths.“It was mostly a shock. I didn’t expect something to happen in that house. Him and Della were the glue to our friend group. We’re all going through a hard time,” Garrett Kowalski, a friend of Della and Sterling, told ABC News’ New Haven affiliate WTNH.The district’s Superintendent of Schools Jeffrey Wihbey said, “Our hearts go out to the students’ family and friends during this difficult time. There is nothing worse that can happen to a school community. Our number one priority right now is doing all we can to support our students, staff and families through this crisis.”Police are investigating the incident and say Jette is cooperating with the probe.The incident is not the first tragedy to strike the Jette family home. Three years ago Sterling Jette Sr., Danielle’s former husband and father to Della and Sterling fatally shot himself after a domestic dispute, police said.Copyright © 2019, ABC Audio. All rights reserved.