CHICAGO (CBS) — Joliet police confirmed that a man shot and killed his longtime girlfriend and their two young children before taking his life Wednesday night.

Autopsies conducted by the Will County Coroner revealed that Brandyn Lee, 34; Jacquelon Gaskin, 28; Gianna Lee, 6; and Giovanni Lee, 1 were all killed by a single gunshot wound.

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Following an investigation, detectives determined Brandyn Lee shot the three others before shooting himself.

“These are the worst types of calls that officers can respond to,” Chief Alan Roechner said. “Anytime a person is killed it’s a heartbreaking situation, but when children are killed, it’s incomprehensible. It is something that I will never understand. My heart goes out to the family of the victims.”

Jacquelon Gaskin, 28, and her two children, 6-year-old Gianna Lee and 1-year-old Giovanni Lee. (Photos supplied to CBS)

Around 10:20 p.m. Wednesday, Joliet police responded to a shooting at a home in the 500 block of Whitley Avenue. Officers found the four dead on the second floor of the home.

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Gaskin’s mother said her daughter and two grandchildren were killed because she was in the process of breaking up with Lee, her longtime boyfriend.

“He was like a controlling type of guy, and I think she was trying to break away from that, and I think that was the trigger, because otherwise why would you? That was his last bit of control, was to take everybody away, not just himself,” Rusha Brooks said. “She was loved, and she is loved by a lot of people, and he just didn’t disrupt his life, he disrupted a lot of lives.”

Gaskin, 28, was studying to become a nurse. Her family said she absolutely doted on her children.

Family members were stunned to learn of the shooting. They thought Gaskin and her boyfriend always had a loving relationship.

“I never seen this coming. I wasn’t aware of this. I seen my daughter on Saturday, smiling, my grandchildren; just like every other time I see her. We did not expect this at all,” Terrance Brooks said.

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Neighbors said they didn’t hear anything unusual Wednesday night. They said the family kept to themselves, and were rarely seen outside the home.