Larry Neuman, 73, was fatally shot Thursday around 1:27 p.m. in the West Garfield Park neighborhood's 4300-block of West Monroe Street.
Neuman was the department's longest-serving bomb technician before he became an explosives specialist for TSA in 2010 after a 28-year career with CPD.
ABC7 was told his shooting death may have happened during an attempted robbery.
Surveillance video released Saturday shows one male wearing dark hoodie with graphic on the back and Jordan shoes.
Video shows 2 suspects in murder of retired officer, CPD says: VIDEO
Another male in the video is wearing an Adidas dark hoodie with Jordan shoes.
Police said both suspects appear to be between 16 and 21 years old.
Now, $75,000 total in rewards are being offered for information in Neuman's death.
The rewards are being offered by the Chicago Police Memorial Foundation, ATF Chicago and FBI Chicago.
Anonymous tips can be submitted at CPDTip.com or by calling crime stoppers at 1-800-535-STOP.
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