CHICAGO (CBS) — A Cook County judge has sentenced a 22-year-old reputed gang member to 125 years in jail for killing a Chicago police officer two years ago.

Shawn Gaston, 22, was convicted of first-degree murder in September in the drive-by shooting death of Officer Alejandro “Alex” Valadez on June 1, 2009.

Chicago Police Officer Alejandro Valadez (Credit: CPD)

Valadez was 27 years old when he was shot in the drive-by shooting in 2009.

He had been on the force for only three years and was working undercover duty on the South Side on June 1, 2009, investigating reports of gunfire when Gaston allegedly gunned him down on the 6000 block of South Hermitage Avenue. Gaston was also found guilty of the attempted murder of an Englewood resident Valadez was interviewing when he was shot.

The courtroom was packed with family, at least 30 officers, Police Supt. Garry McCarthy and others as the judge characterized Gaston as someone who has no respect for police or authority.

“No sentence will ever ease the pain that the Valadez family is feeling now, or ever,” Cook County State’s Attorney Anita Alvarez, accompanied by the slain officer’s family. “But we do hope this sentence does bring somewhat of a little bit of closure to them.”

The defendant maintained his innocence – a sentiment echoed by Gaston’s attorney, John Paul Carroll.

“Some black kid from Englewood gets a fair trial? Only in your dreams,” he told reporters.

Gaston and Kevin Walker, who was the driver of the car, were arrested about an hour after the shooting. They were also responsible for the original gunfire Valadez was investigating, officials said. Walker and Gaston are both charged with first-degree murder.

Prosecutors said a bullet casing was found stuck on the car that Valadez was in. The murder weapon and two other guns were found in the car, which belonged to Gaston’s mother.