In Chicago, some people who saw the immediate aftermath of the shooting described a confused scene with people yelling and police swarming the area.
“People were shouting at each other, because people thought it was a riot, and so did we,” said Gloria Schmidt, who said she had been inside a nearby courthouse and came outside shortly after the shooting. “It was just hysteria,” she said.
Ms. Schmidt’s husband, Jorge Rodriguez, said he saw a man being taken into custody outside the James R. Thompson Center, a Chicago landmark that houses state government offices and a food court that is popular with downtown workers.
“They just seemed to be searching him and taking off articles of clothing,” Mr. Rodriguez said.
Many details of the encounter remained unclear. Superintendent Johnson said it started when officers on routine patrol “observed an individual acting suspiciously,” and walked up to him to try to talk to him.
The man fled, the police said, and Commander Bauer, who was nearby, heard officers giving the suspect’s description over the police radio. When the commander spotted the suspect, Superintendent Johnson said, “an armed physical confrontation ensued” and the commander was shot several times. Superintendent Johnson said the police arrested a suspect and found a gun.
Commander Bauer, who worked for the police department for 31 years, was the highest-ranking officer in the city’s Near North police district, which includes tourist attractions like the Magnificent Mile shopping area and Navy Pier.
Commander Bauer’s death prompted an outpouring of sympathy from elected officials, including Gov. Bruce Rauner of Illinois, who has an office near where the shooting occurred, and Mayor Rahm Emanuel of Chicago, who has faced pressure to reduce the city’s high homicide rate.
“The hearts of every Chicagoan are heavy,” Mr. Emanuel said in a statement.