Photo by Paul Clinton.

Photo by Paul Clinton.

A pair of murder trials began Monday for two men accused of killing a Chicago Police officer who responded to a shots fired call in 2009.

Chicago Police Officer Alejandro "Alex" Valadez died in a volley of gunfire from a passing car as he interviewed a witness after responding to the 6000 block of South Hermitage.

Christoper Harris, Shawn Gaston, and Kevin Walker were later arrested after investigators placed them in the drive-by vehicle. Harris is accused of firing a .40-caliber pistol at the officer from the moving car. Officer Valadez was hit in the left ear and thigh. The first round pierced his brain.

The suspects stashed the car, left their guns in the trunk, and went to a party. Investigators found the vehicle and matched the casings to their guns. Harris had gunshot residue on his hands, reports the Chicago Sun-Times.

Gaston has been convicted and is now serving a 125-year prison sentence. A law named in honor of the fallen officer now requires a minimum of three years in prison for gang members convicted of possessing a loaded gun in a public area.