The gunman who ambushed and shot an NYPD officer sitting inside her mobile command vehicle Wednesday morning, killing her, was a 34-year-old ex-convict out on parole for robbery, officials say.

A motive in the shooting is still not clear, but Alexander Bonds of the Bronx, who also went by the name John Bonds, once ranted online about his treatment in prison and about police getting away with killing people. He had also expressed an anti-government sentiment in online posts, according to a law enforcement official. 

Bonds had been on parole for a robbery case in Syracuse, police said. He had also been arrested six times in New York City, including in 2001 when he kicked and punched police officers while wearing brass knuckles, law enforcement sources told News 4.

#NYPD PO Miosotis Familia has been assassinated in an unprovoked attack on cops assigned to keep NYers safe. Keep her family in your prayers pic.twitter.com/yhRB7H5bvi

— Commissioner O'Neill (@NYPDONeill) July 5, 2017

Prison records show Bonds had a long history of disciplinary problems behind bars, according to The Associated Press. He was written up more than two dozen times while in prison after pleading guilty to a 2005 robbery in Syracuse. Some of the disciplinary knocks are top-level violations such as assaulting an inmate or fighting.

A parole board cited his "poor institutional behavior" and "lengthy history" of arrests in denying his 2012 bid for parole. He was released in 2013 under a provision that sometimes allows parole without a board's input. 

Detectives were searching his apartment in the Longwood section of the Bronx Wednesday, searching for clues as to why Bonds pulled the trigger. He lived at several addresses after leaving prison, including Queens and Manhattan, sources said.

In a video posted on Facebook in September, Bonds ranted about the treatment of civilians by officers and talked about how hard life was behind bars, according to The Associated Press. The photos of Bonds posted on the page match a police mugshot.

"Don't think every brother, cousin, uncle you got that get killed in jail is because of a blood or crip or Latin King killing them. Nah, police be killing them and saying that an inmate killed them," he said in the video.

Aside from the police rant, Bonds' Facebook page mostly consisted of inspirational quotes and quizzes.

Neighbors in the Bronx described Bonds as quiet. 

NYPD Officer Miosotis Familia, 48, was stationed in a mobile command post in the Bronx, looking down and writing in her memo book when Bonds walked up and fired through the passenger side window after midnight, Police Commissioner James O'Neill said. 

Bonds was seen in surveillance footage marching up to the post "with purpose," officials said. 

The bullet struck Familia in the head. Her partner immediately radioed in for assistance. 

An anti-crime team consisting of a sergeant and a police officer who were in uniform encountered Bonds running about one block away from the scene of the shooting, O'Neill said. 

They confronted Bonds, who then took out a gun and pointed it at them. The officers then fired at him and killed him, O'Neill said. A silver revolver was recovered at the scene. 

Another person, believed to be a bystander, was also struck by a bullet in the stomach, police said. The man is in stable condition.

The officer was taken to an area hospital in extremely critical condition, authorities said. She later died. Familia was a 12-year veteran of the NYPD and a member of the 46th Precinct.  

A law enforcement official said the gun Bonds used in the shooting was stolen from West Virginia. Federal ATF agents have been working with the NYPD to trace the history of the gun. Authorities said Wednesday afternoon that the firearm was stolen from West Virginia. 

Bonds was a convicted felon, which means he could not legally purchase a gun and shouldn't have had access to a weapon.