HOUSTON (CN) - A Houston police officer with a history of unjustified shootings and sexual assault shot an unarmed man to death after the man was hurt in a car accident, his mother claims in court.

Patsy Pate, mother of the late Blake Pate, sued Curtis Hampton and the city of Houston in Federal Court.

Pate's son was hurt in an accident on Christmas 2011. His car hit a tree and ended up in a ditch. Hampton, meanwhile, was leaving a nearby apartment complex, Patsy Pate says.

"Officer Hampton witnessed the accident and went to investigate," she says. "The noise of the crash brought numerous residents of the apartment complex outside, allowing them to witness the subsequent events.

"Blake extricated himself from the wreckage of his vehicle and began to walk toward the nearest street light. Blake was stunned from the accident and bleeding from superficial wounds to his face. Blake had his hands extended in front of him.

"Officer Hampton drew his service pistol and fired four shots at Blake at an extreme close range. Blake was struck in the thigh, the chest, and the neck.

"At no point did Blake attack or otherwise threaten Officer Hampton. Blake was not found to be carrying any type of weapon. He was completely unarmed. At the time of the shooting, Officer Hampton was not in fear of his life or bodily injury or that of another. Officer Hampton saw no weapon on Blake nor did he suspect Blake had a weapon."

Blake was declared dead at 12:10 a.m. on Dec. 26, his mother says. He was 24.

"This was neither Officer Hampton's first shooting, nor his first shooting constituting excessive force," Pate says. "On November 11, 2003, Officer Hampton shot Louis Medlow, a 45-year-old man threatening suicide, multiple times in the legs and buttocks.

"Following the shooting, the police department sent Officer Hamilton to a program called 'Crisis Intervention Training' designed to train officers how to appropriately handle mentally disturbed suspects in the least violent fashion.

"This information was the subject of a Houston Police Department Internal Affairs investigation and no finding of excessive force resulted.

"On November 26, 2009, Officer Hampton responded to a call involving a possible dog attack. When he located the dog suspected of involvement, the dog was securely locked behind a chain link fence. The dog lunged at Officer Hampton behind the fence, which prompted Officer Hampton to shoot the dog numerous times. He later falsely claimed he thought it likely that the dog would climb the fence.

"At the time of the shooting Officer Hampton was not in fear of his life or bodily injury or that of another. This information was the subject of a Houston Police Department Internal Affairs investigation and no discipline or retraining of Officer Hampton resulted. The Chief of Police was aware of the shooting and facts and agreed that Hampton's acts were within City policy."

Hampton also has "well-documented" history of sexual assault, Pate says.

"In May or June of 2008, Officer Hampton began to pressure a subordinate into entering a sexual relationship with him. He purchased a bra and panties from Victoria Secret for a subordinate officer and attempted to personally deliver them to her home," Pate claims.

"The female officer refused to answer the door. In December of 2008, Officer Hampton arrived at her apartment and tricked her into granting him access by claiming she needed to sign a department form.

"While inside, Officer Hampton made repeated sexual advances and chased her throughout the apartment eventually causing her to flee into the street. Officer Hampton laughed off the incident, kissed her on the forehead, and left.

"Three days later, the female officer filed a formal complaint against Officer Hampton for attempted rape. Officer Hampton was suspended for fifteen (15) days for this incident but was not the subject of any criminal charges."

Pate says Hampton's 15-day suspension was upheld on appeal because of a similar, previous incident involving him and a subordinate.

"In December of 2007, Officer Hampton awoke his girlfriend, who happened to be another Houston police officer and a subordinate, by handcuffing her to the bed," according to Pate. "At the time, Officer Hampton was wearing a mask and waiving his service pistol around erratically. She repeatedly begged him, 'Don't do this to me.' To silence her pleas, Officer Hampton covered her face with a pillow and attempted to have sex with her while she struggled against him. She was able to end the encounter by biting his penis hard enough to draw blood."

Hampton was suspended for five days for that, but was not charged or arrested, Pate claims.

Pate claims this lack of discipline is part of the Houston Police Department's "long history of condoning and/or ratifying the excessive force of its police officers."

Pate cites 20 incidents, from 1999 to 2011, involving HPD officers using excessive force, shooting or beating suspects, with no repercussions from the police force.

She seeks punitive damages for civil rights violations and wrongful death.

She also sued for ratification, claiming HPD failed to discipline Hampton for her son's death, though his "actions were manifestly indefensible in that the shooting was clearly excessive."