"The entire Chicago Police Department would like to send their deepest condolences" to the family of Thor Soderberg, 43, killed in a parking lot when a 24-year-old man attacked him, grabbed his gun and shot him during a struggle as Soderberg walked to his car after finishing his shift, Assistant Police Supt. James Jackson said.
"We ask that you keep (Soderberg's family) in your prayers," Jackson said.
The unidentified suspect, a convicted felon, ran away after the shooting and robbed a nearby civilian, police said.
Officers from the police station, who heard shots, ran outside and exchanged gunfire with the suspect, shooting him in the abdomen, Jackson said.
The alleged gunman, who was not named because he was not charged in the case, was taken to a hospital where he was under guard Thursday.
The suspect's estranged brother, Calvin Jefferson, 28, said his brother was shot in the chest and was in critical condition, the Chicago Tribune reported.
The suspect was arrested in 2006 for wounding his brother with a .32-caliber handgun, police records cited by the Chicago Sun-Times indicated.
The case was later dismissed, court records indicated.
The suspect's criminal record includes 21 arrests, the newspaper said.
Friends told the Sun-Times and Tribune they considered the suspect mentally disabled, with possible mental illness.
Soderberg was an 11-year veteran, Jackson said. Friends said he was married but had no children.
Soderberg was usually a training academy instructor but was given a one-week assignment to work the street as part of a summer anticrime initiative called Operation Protect Youth.