CHICAGO — The Latest on the shooting of an off-duty Chicago Police officer (all times local):

11:35 a.m.

Chicago Police Superintendent Eddie Johnson says an off-duty officer who was shot in the head is "clinging to life" after undergoing emergency surgery, but that he's hopeful after the 25-year-old man was able to give a thumbs up.

Johnson says there have been no arrests and police haven't identified the person who opened fire on the officer's vehicle at 1:30 a.m. on the city's South Side, a few blocks from department headquarters.

He says detectives are interviewing a woman who was riding with the officer when he was shot and reviewing surveillance video that captured part of the shooting. He says detectives have not determined a motive but suspect it was a case of mistaken identity.

Johnson was emotional as he described his closeness to the officer's just-retired father, and said his own son and the officer work together and are friends.

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8:44 a.m.

Chicago Police say an off-duty officer was shot in the head while driving through the city's South Side and is in critical condition.

Police say the 25-year-old off-duty officer was driving a few blocks from the department's headquarters at about 1:30 a.m. Wednesday when someone in another vehicle opened fire.

Department spokesman Anthony Guglielmi says the officer was rushed to the University of Chicago Medical Center, where he was undergoing emergency surgery.

Police say no arrests have been made.