CHICAGO (CBS) — Chicago Police have increased the reward for information leading to the arrest and conviction of another suspect responsible for the murder of an off duty officer a year ago.

It was on December 29th, a year ago officer Clifton Lewis was working off duty at a convenience store on the 1200 block of North Austin when armed robbers shot him to death.

“We are asking for the public’s help in coming forward leading to the arrest of the offenders involved in the murder of Officer Clifton Lewis,” said Superintendent Garry McCarthy.

McCarthy says he’s hoping this will refresh people’s memories and encourage someone to come forward.

“Today being the one year anniversary with a number of strong leads being pursued by detectives, a year later, we feel it’s an opportunity to advertise a little more. We will not rest until we solve this case,” he said.

Two men have already been arrested in the murder and are awaiting trial. On January 7th, 2012, Edgardo Colon and Tyrone Clay were both charged with First Degree Murder of a Peace Officer and Murder while in Commission of a Forcible Felony.

Police are looking for at least one other suspect. Thanks to the Chicago Police Memorial Foundation, the reward has been increased to $40,000.

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