CHICAGO (CBS) — Two men accused of killing Chicago Police Officer Clifton Lewis during a holdup at a West Side convenience store late last year were formally charged with murder on Friday.

Edgardo Colon, 34, and Tyrone Clay, 29, are both charged with first-degree murder of a peace officer for the Dec. 29 murder at the M&M Quick Foods at 1202 N. Austin.

On Friday, both were indicted on the charges and arraignment was set for Feb. 21, Cook County State’s Attorney’s office spokeswoman Tandra Simonton said.

Police have said two masked men walked into the store in the Austin neighborhood near Oak Park and robbed it.

The bandits got away with hundreds of dollars. Lewis, who was working as a security guard at the store, fired a shot before one of the robbers opened fire on him with a TEC-9 semiautomatic weapon with a high-capacity clip, sources said.

Lewis’ weapon is missing, along with the TEC-9, sources said.

Colon and Clay were among four men police initially questioned in the case. The other two were released without charges.

Officials at the time said the investigation remains open and detectives are seeking anyone who may have known about the plan to rob the store.

Colon is a parolee who was in a car that police stopped for making an improper turn. Police found a .357-caliber handgun with two live rounds in the car.

(Source: Sun-Times Media Wire © Chicago Sun-Times 2012. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)