The children's aunt says all six children witnessed Sunday's killings, and that the security guard may have saved their lives

Six children in California are now orphaned after a double murder-suicide Sunday also claimed the life of a security guard who tried to intervene in what police described as a domestic dispute.

According to a statement from the San Jose Police Department, 29-year-old Erica Chanon Pantoja's estranged husband, Salvador Pantoja, 33, showed up outside her apartment building early Sunday morning, and the two had an argument in the parking lot.

Security guard Marco Carral Duran, 23, was working nearby, heard the couple fighting, and attempted to intercede, police said.

"The suspect shot the uninvolved male at least one time and then shot the female as well," reads the San Jose Police statement. "The suspect was found at the scene deceased from a self-inflicted gunshot wound."

The statement notes "the motive and circumstances surrounding the incident are under investigation."

Maria Chanon, the aunt of the couple's children, spoke to ABC 7 News, and said they witnessed their mother's murder.

"The oldest one who saw the whole incident, she still cries," Chanon said, adding her sister was planning on divorcing her killer. "She can't understand why her father would do that."

Chanon said she believes Duran saved the children — who're aged 1 to 10 — giving them valuable time to escape the deadly situation.

Meanwhile, the San Jose Police Officers' Association Charitable Foundation has established a special fund for the six kids