CHICAGO (STMW) — A 50-year-old woman convicted of killing a Chicago Police officer with his own gun during a disturbance on a CTA bus will spend the rest of her life in prison.

Robin Johnson was sentenced to natural life plus 15 years for the fatal shooting of Officer Robert Francis in the early morning hours of July 2, 2008, according to the Cook County State’s Attorney’s office. She was convicted of murder by a jury in October 2012.

Francis, 60, was responding to a call of a disturbance on a bus at Belmont and Western. Prosecutors said he responded to the call alone, not realizing the danger.

Within seconds, the 27-year Chicago Police veteran was dead.

Johnson disarmed and shot the uniformed officer after he confronted her for the run-in she’d had with another woman on a CTA bus.

Johnson was “aggressive, hostile and angry,” prosecutors told jurors during her trial.

Before Francis arrived, Johnson was seen holding her own breast, telling the commuter, whom she didn’t know, “You made me this way,” prosecutors said.

Johnson was pacing back and forth, stomping her feet and talking to herself outside the bus, which witnesses saw her getting in and out of, while pressing up against the other woman, prosecutors said.

When the officer arrived, he was flagged down by the bus driver, and attempted to calm Johnson down, prosecutors said. But she became combative and attacked the officer.

Both fell to the ground, Johnson grabbed Francis’ gun, and though he had his hands up in the form of “a surrender,” she shot him in the face at point-blank range, prosecutors said.

A defense attorney implied that Johnson may not have had her finger on the trigger and the gun could have went off during the tussle, but witnesses said they saw Johnson with the weapon and that she knew what she was doing.

Johnson allegedly shot Francis two more times while he lay motionless on the pavement.

She was also convicted of one count of aggravated discharge of a firearm, which resulted in the additional 15 years, prosecutors said. She was acquitted of attempted murder and aggravated discharge of a firearm for allegedly shooting at Francis’ colleagues, who returned fire and wounded Johnson.

(Source: Sun-Times Media Wire © Chicago Sun-Times 2014. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)