09/22/2011 09:40 am ET Updated Dec 06, 2017

Shawn Gaston Allegedly Partied After Fatally Shooting A Chicago Police Officer (VIDEO)

A man who allegedly killed a plainclothes Chicago Police Officer in the early morning hours of a summer's day in 2009 was reportedly drinking tequila and partying with friends a matter of minutes after the shooting, prosecutors said during his trial Tuesday.

Shawn Gaston, a reputed gang member, was charged two years ago with murdering 27-year-old three-year veteran Alejandro "Alex" Valadez. According to an AP report, Valadez was interviewing a resident near the corner of 61st and Hermitage in Chicago's Englewood neighborhood while investigating reports of gunfire in the area. Gaston, then 20 years old, allegedly shot at Valadez from a car driven by his friend, Kevin Walker. Valadez was struck in the head and leg and died that day.

(Scroll down to watch a video report on the first day of Gaston's trial.)

In a packed courtroom Tuesday, Cook County State's Attorney Anita Alvarez claimed that Gaston was partying at a neighbor's home within minutes after shooting Valadez and narrowly missing Kelvin Thomas, the resident that the officer was interviewing, according to the Chicago Sun-Times. Gaston and his friends were reportedly retaliating against members of a rival gang, who fired at them earlier.

The trial marks the first case Alvarez is prosecuting since she was elected in 2008.

"This guy went to 62nd and Paulina and started to party because that's what you do after you shoot," Alvarez told jurors Tuesday, as reported by NBC Chicago.

Gaston's attorney John Paul Carroll says his client is innocent and was framed by police, though Alvarez said she has a videotaped confession from the defendant. He twice described the investigation of his client as a "lynching," according to WGN. Carroll also argues that no DNA evidence has linked Gaston from weapons recovered at the scene of the crime.

Two other alleged participants in the crime -- Walker and Christopher Harris -- are still awaiting trial.

WATCH: NBC Chicago's report on the Gaston trial:

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