NBC Los Angeles An undated photo of Alesia Thomas, who died in an LAPD patrol car in 2012 after a struggle with police.

Prosecutors have filed an assault charge against a Los Angeles police officer for her alleged role in a 2012 incident captured on squad-car video in which a 35-year-old mother died after a violent struggle to place her in custody.

Officer Mary Margaret O'Callaghan, a 19-year veteran of the force, is charged with assault under color of authority for kicking Alesia Thomas in the groin and stomach during the attempted arrest on July 22, 2012, which involved at least three other officers.

Assault under color of authority carries a maximum penalty of three years in state prison. Prosecutors have asked for bail of $35,000. O'Callaghan, 48, has been relieved of duty without pay and also faces possible departmental sanctions.

Prosecutors allege that O'Callaghan used criminally excessive force as she and several of her colleagues attempted to place Thomas in custody during an investigation of alleged "child abandonment."

Thomas, who according to her autopsy report suffered from drug addiction, bi-polar disorder and schizophrenia, had dropped off two of her children -- ages 3 and 12 -- in front of an LAPD station in South Los Angeles.

A short time later, LAPD officers caught up with Thomas at her home and she told them she could no longer take care of her children, according to a use of force report prepared by the Los Angeles Police Commission.

The report details officers struggling with the 6 foot, 228-pound woman as they attempted first to handcuff her and then place her in restraints and eventually into a squad car, where the encounter was captured on video and audio from a Digital In-Car Video System activated by the officers. Throughout the report, O'Callaghan is referred to as a male and as “Officer D.”

Read the report here

It was in the late stages of that confrontation that officials say O'Callaghan swore at Thomas and slammed her left foot into her groin and thigh area.

Moments after officers shut the patrol car door, Thomas could be seen moving around and trying to sit up before her eyes rolled back and she slumped toward the driver's seat, the report states.

The Los Angeles County Coroner said while the struggle with police could not be excluded as a contributing factor, the manner of death was "undetermined." Cocaine intoxication was listed as a major contributing factor.

In the use of force report, LAPD Chief Charlie Beck and the civilian panel that oversees the department found the officer violated department policy in how she used her feet to kick and push Thomas and showed "apparent indifference...toward the Subject during the contact, including the nature of the comments that were made.”

Citing the criminal case, authorities said they would not release video of the incident, which also continues to be under administrative review.

O'Callaghan's attorney could not immediately be reached for comment.

Tyler Izen, president of the Los Angeles Police Protective League, the union that represents the department's 10,000 officers, would not offer specific comments on the incident because he had not seen the video and the officer has retained her own legal counsel. But he noted the allegations seemed out of character for a veteran officer who was dedicated to the community she served.

"The alleged actions of the officer are incongruous with her reputation as an officer who was known to be diligent, courteous and ethical," Izen said. "This officer had previously been publicly commended by the LAPD for community efforts and was publicly commended for helping a burglary victim’s family who lost all their presents at Christmas time.”

"In commending her," he noted, "the department said, 'This is yet another fine display of the professional attitude displayed by the men and women at the Los Angeles Police Department Southeast Division, placing the interest of the community first.'”

Criminal prosecutions of police officers are rare in part because of the broad protections offered peace officers under state law and the quality of evidence needed to secure a conviction in court.

At the LAPD, few officers have been criminally charged over the last 25 years. Four officers were charged with assault after the infamous 1991 Rodney King beating. The men were acquitted in a state trial, but two were found guilty of violating King’s civil rights in a federal trial.

In 2006, LAPD officer Sean Joseph Meade was caught on videotape applying a choke hold and punching a handcuffed 16-year-old boy. Meade was charged with felony unlawful use of force and eventually pleaded guilty to two misdemeanors in a deal in which he agreed to resign from the force.

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