The father of three children who were allegedly killed by their mother last year has filed a lawsuit against the city and county of Los Angeles, accusing police and social workers of failing to intervene to protect his young daughters and son before their deaths.

Erik Denton filed the lawsuit Thursday in Los Angeles Superior Court, more than a year after the children were found dead in a Los Angeles apartment. Denton’s ex-girlfriend and the mother of his children, Liliana Carrillo, fled to Tulare County, nearly 200 miles (322 kilometers) north of the scene.

Carrillo, later told KTLA sister station KGET that she wanted to “protect” her kids from alleged abuse amid a bitter custody battle. She admitted to drowning her daughters, 3-year-old Joanna and 6-month-old Sierra, and her 2-year-old son, Terry, in the jailhouse interview.

Carrillo is charged with three counts of homicide and her case remains ongoing, according to online court records. She is scheduled to return to court next month and is being held in jail on more than $6 million bail. The public defender’s office, which is representing Carrillo, did not immediately return a request for comment Thursday.

Denton sought custody of his three children last year, citing what he said was their mother’s erratic and unstable behavior and mental health issues. Fearful for their safety, Denton petitioned the court for custody, alleging Carrillo was delusional and had taken the kids and refused to tell him where they were.

Carrillo then filed a restraining order against Denton and claimed he was an alcoholic who may have sexually abused their eldest child.

As the case wound through family courts in Tulare and Los Angeles counties, the parents traded accusations in dozens of pages of documents. Police were called, social workers were consulted, alarming text messages and Facebook posts were saved as legal exhibits.

Within weeks, the children were dead. Denton’s lawsuit alleges that Los Angeles Police Department officers and social workers from the county’s Department of Children and Family Services repeatedly ignored warnings about Carrillo’s behavior and failed to investigate and cross-report their findings to other agencies as required under state law.

“The murders of Erik’s three children would have been prevented if law enforcement officers and child welfare workers did what they were required to do by law, which is to step in and protect children who are at risk of abuse or neglect,” said David S. Casey, Jr., who is representing Denton, in a statement.

The Los Angeles County Department of Children and Family Services declined to comment on the allegations, citing the pending litigation and confidential records, but offered the agency’s condolences to the Denton family.

“Our mission to protect children is one we share with our partners in law enforcement and the community,” the department said in a statement. “We remain fiercely committed to strengthening our community partnerships to enhance the safety net for children and families.”

The Los Angeles city attorney’s office said it will review the lawsuit and declined further comment.

Representatives for the Los Angeles County counsel and LAPD did not respond to requests for comment on the lawsuit on Thursday.