He started his criminal life as a juvenile, authorities said, selling marijuana before graduating to more serious offenses.
He racked up 11 arrests, two of which landed him in state prison, according to Los Angeles County Sheriff Jim McDonnell.
On one occasion, he pointed a handgun at an off-duty USC security officer near campus and robbed him of his wallet, cellphone and watch.
When LAPD officers caught up with him a week later, he was still wearing the stolen watch.
On Thursday, authorities identified Trenton Trevon Lovell, 27, as the man who shot and killed a sheriff's sergeant responding to a burglary call in Lancaster earlier this week.
Lovell used a stolen handgun to wound Sgt. Steve Owen, then executed the lawman by standing over him and pumping four more bullets into his body, McDonnell told reporters at a news conference.
"This was an individual who was certainly the aggressor, someone who was truly a predator," McDonnell said.
The sheriff said it was time for a serious conversation about policies that he blamed for allowing the gunman to cycle in and out of custody for years.
Residents of the apartment complex where Owen was killed said Lovell sometimes stayed in one of the units with his sister.
Blanca Oseguera, 38, echoed the sentiments of a small crowd of neighbors who said none was surprised to hear Lovell's name linked to the shooting.
Oseguera said she was involved in a confrontation with him weeks earlier, after he cursed at her daughters while he smoked marijuana outside.
"I told him, 'You shouldn't be here; you don't live here,' " she said.
Oseguera and another woman, 26-year-old Cynthia Appleby, said Lovell was known to have a "hot temper" and Oseguera's clash with him three weeks ago was witnessed by several neighbors.
Lovell's aunt, Deborah Matute, said she hadn't seen her nephew since he moved out of her Harvard Heights-area apartment in Los Angeles earlier this year.
Matute said she didn't know details about his past troubles with the law and never asked him about them. She allowed him to stay with her family around April and May because he needed an address where his parole officer could visit him, she said.
"I just felt sorry for him," she said. "I just didn't want to see him in the street."
When Lovell lived with her, there were no problems, Matute said. He would stay the night at the apartment and then mostly be out.
"He's a nice person when he wants to be," she said.
But after police came to the apartment wanting to search it, his family asked him to leave in June.
"I didn't want that kind of problem here," she said.
Matute said she didn't see Lovell again until Wednesday afternoon, when she recognized his face on television as she watched news about the slain sheriff's deputy.
"What have you done now?" she thought to herself.
"I just couldn't believe it. I was shocked," she said. "I'm sorry for the police officer's family. I'm sad for them."
She stood quietly for a minute, shaking her head as she thought.
"I don't know what to say," she said.
Wednesday's shooting occurred shortly after noon as Owen, 53, and another deputy responded to a 911 call from a woman reporting a burglary at a residence in the 3200 block of West Avenue J-7, authorities said. As Owen went to the rear of a nearby apartment complex, he was confronted by Lovell, sheriff's officials said.
According to authorities, Lovell shot the sheriff's sergeant and ran toward the front of the apartment building.
A second deputy arrived at the complex and confronted the gunman, who had entered Owen's sheriff's cruiser and was trying to steal it, sheriff's officials said.
The deputy opened fire on the cruiser, but Lovell threw the car into reverse and rammed a second patrol car, which struck the deputy and injured him, authorities said. Lovell was shot and wounded in the shoulder.
He jumped out of the cruiser and ran into a nearby home, where two teenagers were inside. One teen was able to send a text message to his mother, who alerted authorities.
Sheriff's SWAT deputies entered the home to rescue the teens. Lovell fled out the back and was captured after he jumped over a fence into a neighboring backyard, authorities said.
Lovell's rap sheet dates back years, according to court records. In 2008, he pleaded no contest to resisting arrest and was given a 90-day jail sentence. Months later, he was arrested and later convicted of the robbery near USC. He was sentenced to six years in prison, according to Los Angeles County Superior Court records.
Last year, he pleaded no contest to driving under the influence of alcohol and causing injury to another person, court records show. Lovell was ordered to complete a nine-month first-offender program for drunk drivers and enroll in a drug and alcohol counseling program. He was scheduled to appear in court Oct. 24 for a progress report.
Elliott Coney, the former USC security officer who was robbed near campus in December 2008, recalled Thursday how Lovell had entered his car and put a gun to his chest, demanding his valuables.
Lovell appeared annoyed after Coney told him that he had nothing. He leveled the gun at Coney's face.
"I thought for a second he was going to shoot me," Coney said.
He gave Lovell his wallet, containing $300 to $400, along with his cellphone and watch. Lovell jumped out of the car and walked away in front of the vehicle, as if to show he was not concerned about getting caught, Coney said.
Coney reported the robbery to Los Angeles police and told them that he could identify the gunman. Days later, Coney was driving to campus and spotted Lovell with a group of men.
He notified the LAPD. Days later, Lovell was arrested, records show.
Coney, 34, said he was stunned to learn that Lovell was identified as the man who shot and killed the sheriff's sergeant's this week.
"It puts things into perspective, how blessed I am," Coney said. "I could have lost my life."
Times staff writers Nicole Santa Cruz and Richard Winton contributed to this report.
7:00 p.m.: This article was updated throughout with more details about Lovell's history and comments from the county's sheriff and a former robbery victim of Lovell's.
1:50 p.m.: This article was updated with comments from Lovell's mother, an aunt and neighbors in the apartment complex where he was staying.
12:50 p.m.: This article was updated with comments from neighbors.