The jury of six men and six women reached a verdict against Steven Montano after less than two hours of deliberating Monday.
Jurors had the option to consider second-degree murder, but did not.
Chicago Police Superintendent Larry Snelling and Cook County State's Attorney Eileen O'Neill Burke spoke after the verdict.
Cook County SA, CPD supt. speak after guilty verdict
Vásquez Lasso's relative stood with them, and said justice had been done.
"The only thing we that we can do for the family now is to bring some level of justice, and they got that today. It was very important," Snelling said.
"I think the jury saw it for what it was, and it was a 'hail Mary' defense, and it did not convince the jury of anything," O'Neill Burke said.
Chicago Fraternal Order of Police President John Catanzara and CPD Officer Carlos Yanez Jr., who was critically wounded in a shooting the killed his partner, Officer Ella French, also spoke.
"That's sadly forgotten quite often in this city the level of danger that our officers and members are exposed to every single day, every shift," Catanzara said.
Wounded CPD Officer Yanez, FOP President Catanzara speak after guilty verdict
In court, Montano's eyes widened, as the jury found him guilty of first-degree murder.
Jurors also heard closing arguments before starting deliberations Monday afternoon.
RELATED | Widow of slain CPD Officer Andrés Vásquez Lasso first to testify in accused murderer's trial
Prosecutor Sara Grgurovic argued, "Officer Vásquez Lasso was a uniformed officer chasing a suspect. You do not get to shoot the police."
Montano's attorney Brett Balmer told jurors, "He was running away because he was afraid for his life."
But prosecutor Kevin Nolan called Montano's version of events a "nonsensical claim." They called Montano Vásquez Lasso's "angel of death."
There were about four days of testimony from over a dozen witnesses in the roughly one-week case at the Leighton Criminal Courthouse.
SEE ALSO: Suspect testifies in own defense in trial for murder of Chicago police Officer Vásquez Lasso
Vásquez Lasso's widow was among those who testified.
Jurors also saw police body camera video, even from Vásquez Lasso. It captured the deadly encounter and aftermath.
Chicago police officers and Gold Star families accompanied 32-year-old Vásquez Lasso's family in court Monday.
Montano took the stand in his own defense last week, telling jurors that he was afraid of police and that it was "not his intention" to shoot an officer that day in March 2023.
Montano testified he was trying to hide his gun, and didn't know it was an officer telling him to stop several times.
But prosecutors say Vásquez Lasso was shot five times during the Gage Park domestic disturbance call.
Montano's girlfriend had called police to say he threatened her with a gun.
Montano was 18 at the time of the fatal shooting. Vásquez Lasso shot him in the face during the incident.
Montano's family and attorneys left without comment.
He's due back in court Sept. 3 for post-trial motions.
"While this first-degree murder of a police officer conviction does not bring back fallen Officer Andrés Mauricio Vásquez Lasso, it does offer a small measure of justice.
"Each day since we lost Andrés, his family has had to relive the trauma of what they experienced on March 1, 2023. We cannot and will not forget the sacrifices that they also made for our city amidst his loss.
"Andrés was a courageous officer who protected the people of our city, even in his final moments. Though this trial is over, we will honor Andrés' legacy by carrying on his mission of service."