Updated

Investigators are trying to piece together the final moments of three children who were killed when they arrived home with their mother to find a gunman waiting inside their Albuquerque, New Mexico home, officials said Tuesday.

Albuquerque Mayor Richard Berry described the shooting as s  "senseless and tragic act of violence," and called for the city to come together.

"It's hard not to be angry. It's hard not to be frustrated," he said during a news conference at police headquarters.

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Authorities said the incident took place around 6:30 p.m. Monday when a woman called for help, saying shots had been fired at the home in southeast Albuquerque.

Officers arriving at the house found the 37-year-old mother and three children — a 5-year-old boy, a 6-year-old girl and a 9-year-old boy — all shot, police said. The victims were rushed to the hospital, where the children were later pronounced dead.

The mother remained in critical condition Tuesday afternoon and investigators have not been able to talk to her, according to police. They said she's the only surviving witness.

Albuquerque Police Chief Gordon Eden said preliminary evidence suggests the family was attacked by George Daniel Wechsler, 45, who was believed to have had a brief relationship with the 36-year-old mother. Wechsler was found unconscious at the home with a self-inflicted gunshot wound and was taken to a hospital, where he later died.

Eden said Wechsler broke into the home and waited for the mom and children to come home. Police said Wechsler had asked to visit to give the children Christmas gifts but the mother told him no after he repeatedly called and sought to visit. The mother had asked Wechsler several times to stay away, police said.

It was not clear in what order the victims were shot, but Eden said the mother was wounded as she tried to get the children out of the home.

“The mother was attempting to save one of her children while she was critically injured herself,” he told reporters.

Neighbors told KRQE-TV they didn't typically see children at the home, but toys and playsets were spotted in the backyard by television news crews.

The shooting drew condemnation from New Mexico Gov. Susana Martinez.

"I'm heartbroken over this horrible and senseless act of violence that has left all of us shaking our heads and asking 'Why?" Martinez said in a statement. "My heart and prayers go out to the family and the mother who is fighting for her life."

Authorities said there was no history of previous calls to the home.

Police have not yet released the names of the mother or children involved, saying it is still too early into the investigation and that some family still has not been notified.

Officials with the Albuquerque school district said their crisis management team and other support staff were ready to help classmates of the victims and staffers.

The Associated Press contributed to this report.

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