Commander Paul Bauer, 53, was struck multiple times and died from his wounds at a hospital yesterday.
"It's a difficult day for us," Johnson told a news conference, fighting back tears.
Patrol officers had approached a man in the street last afternoon who was described as acting suspiciously. The man physically fought with the officers and fled, according to Johnson.
Bauer, a 31-year department veteran who heard a description of the suspect over police radio, was nearby.
"He observed the offender," Johnson said. "An armed physical confrontation ensued."
The shooting occurred on the lowest floor of the Thompson Center, a busy state government building where dozens of agencies are located.
Added Chicago Mayor Rahm Emanuel: "(Bauer's) death is a tragic reminder of the dangerous duty the men and women of our police department accept to ensure the safety of us all.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)