The family of a man with mental health problems who died after an encounter with Whittier police last spring filed a $15 million legal claim against the department Wednesday, saying officers "brutally killed" him after being called to help transport him to a psychiatric hospital.

Jonathan Salcido, 27, died at a hospital May 4, shortly after the incident, which ended with officers wrestling with him on the ground. An emergency room physician noted "asphyxia" as the cause or contributing cause of death, along with head trauma and "traumatic" arrest, according to the family’s claim. A legal claim typically precedes a lawsuit.

His mother Jasmin Salcido said in the claim that she witnessed officers "piled on top" of her son, who already was handcuffed. As she sought to intervene and explain her son was mentally ill and unarmed, she said she was told, "let police do their job."

“My son is dead, and no one will tell me why," said Jonathan's father Gary Salcido during a news conference outside Whittier police headquarters. "He was vulnerable, sick, defenseless, and my wife asked for help. And instead of help, he was killed by the police, by the very people who are supposed to protect us.”

Whittier police were "well aware" of her son’s medical condition, said Jasmin Salcido. She and her husband had called officers to the family home where Jonathan lived all of his life several times - either to help locate him after he had gone missing or for help getting him to a psychiatric facility.

Whittier Police Department spokesman Officer John Scoggins said in an email that the Salcido incident "was a tragic event and is being investigated by the Los Angeles County Sheriff’s Department and the Los Angeles County District Attorney’s Office. Please refer any case inquiries to these agencies."

The sheriff typically takes at least six months to investigate an officer-involved shooting and the DA can take more than a year to determine if it was a legal shooting.

There's no mention of the incident on the Whittier Police Department’s website or Facebook page, which in the days following Salcido’s death focused on recruitment efforts, an armed robbery and bike safety month.

“My brother’s voice and his life was taken that day, and I will be his voice,” said Jennifer Chavez, Jonathan’s older sister. “I am here because I want justice for Jonathan.”

Around his 18th birthday, Salcido was diagnosed with mental illness that was variously characterized as bipolar disorder, paranoid schizophrenia, or schizoaffective disorder, according to the family. Over the years, he’d been hospitalized on "numerous occasions" on both a voluntary and involuntary basis.

His behavior had become increasingly erratic in the days prior to May 4 and his parents concluded he needed to be hospitalized again for an adjustment to his medication. Salcido initially "reacted well" to this information but became agitated the morning of the appointment. Jasmin Salcido said when she called police for help once again, he said he was afraid of them and ran out the door.

His mother went after him, telling a 911 operator where they were as she followed him down the street. Police arrived as Salcido was trying to climb over a fence. They "descended on him … pinning him face down" on the concrete instead of waiting for paramedics or "calmly attempting to subdue him," according to the family's claim.

Her son was "clearly panicked" as she heard him "scream out in terror" – his legs "frantically thrashing" back and forth under the weight of officers, the claim states.

"Suddenly, Jonathan stopped moving. The police got off of Jonathan … one officer stated, 'he’s not breathing,'" it says.

This is not the first time a family's call to police for help with a mentally ill loved one has resulted in officers either killing or seriously injuring the individual.

Mental health issues were noted in at least 41 officer-involved shootings in L.A. County between 2010 and 2014, according to a KPCC analysis of official case summaries from the D.A.’s office. At least a dozen shootings occurred after friends, family and even mental health professionals called for help, KPCC found.

"Justice demands that the Whittier Police Department train its officers how to de-escalate encounters with people with mental illness," said attorney Dan Stormer, who represents the family.

He also called on the district attorney to prosecute the police officers involved in the incident to be prosecuted for "their cruel, excessive and unnecessary use of force.”

This story has been updated.