A man is suspected of shooting and killing his girlfriend's teenage son and daughter at their Watertown, Connecticut, home Tuesday night after an argument about him smoking cigarettes in the house escalated, according to police. They said the man had moved into the home just two weeks earlier.

He died of an apparent self-inflicted gunshot wound, according to Watertown police.

“The boyfriend moves in the house two weeks ago for the holiday season. He’s gone and both her children are gone,” said Watertown Police Chief John Gavallas. “This mother is completely distraught as you can imagine.”

The teens’ mother, Danielle Jette, called 911 at 9:45 p.m. and told dispatchers that her live-in boyfriend had just shot her daughter and son, police said.

Officers responded to the home on Litchfield Road and searched room by room. First they found the suspected shooter, 42-year-old Paul W. Ferguson, dead in the master bedroom.

Officers found the 15-year-old daughter, Della Jette, on the deck with a gunshot wound to the chest.

Her 16-year-old brother, Sterling Jette Jr., was found between the kitchen and living room with a gunshot wound to the chest.

Police said Della had gone on a school field trip to New York earlier that day and had a discussion with her mother when she got home about Ferguson smoking cigarettes in the house and that discussion got a little loud.

Ferguson, who was downstairs watching TV with Sterling, went upstairs and told Della to quiet down and not speak to her mother that way, and that led to a “dust up,” police said during a news conference.

Ferguson then 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 said.

As the mother was going downstairs to call 911, she heard another gunshot.

Police believe that Ferguson shot Della on the deck, then went back into the house and shot Sterling in the chest.

Police said Ferguson, a convicted felon, then closed himself in a bedroom and apparently shot himself. Because of his criminal background, he would not have been allowed to possess a firearm, according to police.

Waterbury Police

Police said Ferguson had been charged with larceny in the third degree in Naugatuck in February 2014 and failure to appear in April 2014.

Waterbury police said he was arrested in May 2014 on charges of a probation violation and failure to appear.

Both teens were transported to Waterbury Hospital, where they were both pronounced deceased shortly after arrival.

“Unfortunately, their wounds were so serious that it was futile,” said Gavallas.

Ferguson had been dating the victims’ mother for around two years and moved into the residence about two weeks ago, police said.

The mother is cooperating with the investigation.

“She was shocked. Absolutely shocked,” said Gavallas. “This mother is completely distraught as you can imagine.”

The teens both attended Kaynor Technical High School in Waterbury and have close ties to the Watertown and Woodbury school communities, police said. School officials have been notified to provide services to peers and a crisis team is being sent to the school.

With the help of Sterling’s friends, his employer, a local landscaping company, created a makeshift memorial along Main Street in Watertown. Friends and family members gathered to share memories of two lives taken too soon.

“He was so loving and caring, said Sterling’s girlfriend Melanie Lopez. “He was such a great person. He didn’t deserve this.”

“She was my best friend. She was like a sister to me. Her and her brother were like a second family. I’m going to miss everything about them,” added Shaylyn Fisher, Della’s best friend.

Garrett Kowalski helped set-up the memorial and organize a candlelight vigil Wednesday night. His mother, Melissa DeFranco, said they boys were best friends, and Sterling was like her second son.

“My son’s friends are never gonna walk through our door again,” she said through tears. “He’s always saying, ‘Ma you got any cereal for me?’ I’m not going to be able to answer that question.”

DeFranco went to the hospital Tuesday night with her son, after he received word of the shooting, but didn’t receive the news she was hoping for. As a mother, she said she cannot imagine what the children’s mother is facing.

“Your kid’s not coming home anymore and that’s the worst fear of any parent out there,” she said.

A sophomore at Kaynor Technical High School in Waterbury, Della was studying to become an electrician. Her uncle described Della as an angel.

“She was always so caring and loving for everyone and she was always passionate about everything that she did,” added her good friend Jordan Hurley.

Sterling’s friends said their favorite memories involved working on tractors together in their garages. He was a junior studying mechanics.

“I was really heartbroken. He was a wonderful person, had an absolute heart of gold,” said Beck Curtis. “He was one of the nicest people I knew. I think despite all the circumstances in his life he could always put on a smile, work hard, and showed people he cared about them.”

Lopez said he argued with Ferguson, but there were no red flags.

“It would never be anything serious. There was never any violence involved ever, so this is a shock. This is surprising to me,” she said.

Fisher, who has known Della for more than a decade said she also talked about getting into arguments with Ferguson.

“Sunday night we were texting and she said that they got in a fight, but I didn’t ask her about it because I could tell she was hurt by it,” she said.

Tuesday’s tragedy wasn’t the first Danielle has faced. Three years ago her husband, Sterling and Della’s father, shot and killed himself in the same home as Tuesday night’s tragedy, according to police.

“There would be nights where he would just be upset and cry over how he misses he dad, and I’ve kind of come to the realization that now he’s with his dad and now he doesn’t have to miss his dad anymore,” said Lopez.

The superintendent of schools in Watertown released a statement on Wednesday morning.

“The Watertown community has suffered a tremendous loss. Two former students were tragically killed last night in a shooting at their home. Although the two siblings who were killed were not enrolled at our High School, they attended Watertown schools through eighth grade and formed close relationships with students and staff over the years. This morning, crisis teams are in place at Watertown High School and Swift Middle School to support students and staff as they grieve,” Supt. Rydell Harrison said in a statement. “Our school community, like the wonderful town we live in, will come together to do everything we can to provide support to our students, staff and families during this difficult time,” the statement goes on to say.

Watertown detectives, the State Police Western District Major Crime Evidence Collection Unit and the Waterbury States Attorney’s Office are investigating.

The Office of the Chief Medical Examiner’s Office is also investigating.

“The deaths of these children is a tragedy for our whole community and the police department extends our deepest sympathy to the victims mother, family and friends,” police said in a statement.

A vigil for the Jette family will be held at 6 p.m. at Our Savior Lutheran Church at 505 S. Main St. in Thomaston. A candlelight vigil was planned for 7:15 outside the memorial on Main and Trumbull streets. Another memorial was planned for Friday, December 6 at 6 p.m. in Watertown’s Veterans Memorial Park.

SUICIDE PREVENTION HELP: The National Suicide Prevention Lifeline (800-273-8255) is open 24 hours a day, 7 days a week.