The man accused of killing a mother and three of her children in a Pembroke Park shooting has died, according to the Broward Sheriff's Office.

Stephen McKenzie, 34, who shot Julia Cruz, 32, and her four children—killing three of them—before turning the gun on himself, succumbed to his injuries on Thursday, March 27.

Authorities said McKenzie was found critically wounded after the attack and was taken to HCA Florida Aventura Hospital, where he later died.

The massacre unfolded Wednesday, March 26, at the Sundrift apartment complex on West Hallandale Beach Boulevard, just after 7:30 p.m. When officers arrived, they discovered Cruz and three of her children—2-year-old twins Nova and Emery McKenzie and 11-year-old Xion Solomon—dead inside unit 408.

Eight-year-old Phiinyx Solomon was also shot but survived. She remains in serious condition at Joe DiMaggio Children's Hospital.

"They were my oxygen"

As loved ones reel from the tragedy, Cruz's mother, Irma Rivera, is struggling to comprehend the loss.

"My daughter, my grandkids were my oxygen, so right now, it's hard to breathe," Rivera said.

Rivera described Cruz as a devoted mother who put her children above all else.

"She was a hard-working mom, she wouldn't trust her kids with anybody. She was very devoted to her children," Rivera said. "The two little ones, Emery and Nova, were so adorable. They were so happy children and I miss them terribly."

Rivera also revealed that Cruz had confided in her just days before the shooting.

"My daughter just called me and told me she was exhausted from the mental abuse," Rivera said. "It was up and down a lot. There was no history of physical abuse. She called me on Tuesday that she was going to leave him this weekend. On Wednesday, I did not get to speak to her and that's when it happened."

A brother's final act of bravery

Xion Solomon, the eldest of the four children, died trying to protect his mother and sister. His grandmother, Rita Hanson, said he acted selflessly in his final moments.

"He was really special, and he was a good kid. He was always protective of everybody—all his brothers, all his sisters," Hanson said. "He was just doing what Xion does, just trying to, you know, just be the protector that he is."

Kelvin Solomon, Xion's father, echoed the sentiment, calling his son a hero.

"He was a hero, and I want everyone to know he was a hero. He died protecting his mom and his sister," he said.

Unanswered questions

The Broward Sheriff's Office has not yet determined what led McKenzie to open fire. A relative of Cruz told CBS News Miami that she had been trying to leave him.

Solomon acknowledged that he was aware of difficulties between Cruz and McKenzie at home.

For now, the family is left grieving the lives lost—and holding on to the memories of a mother and children taken too soon.