Investigators are trying to contact him, and say he may face child endangerment charges.
Andrew Holmes, an anti-violence activist in Chicago, said police received several calls from the community about the man in the Facebook photo.
"We are getting loads of calls that have been coming in, saying they may know who this individual is, they may know who the child is," Holmes said. "It's about putting the guns down, saving a child's life. This is not about getting anybody in trouble, because, you know, you put that on Facebook yourself."
It's unclear whether the gun in the photo is real, but the child's finger is close to the trigger. Holmes said that part of the picture is incredibly disturbing.
The photo surfaced just a week after a 3-year-old boy accidentally shot himself in the head while playing cops and robbers in the city's Englewood neighborhood.
"Whether it's an air gun or a real gun in her hand, she's taking a selfie with a man and she's got her trigger finger on the trigger," Holmes said. "If she goes to a relative's house and there's an unsecured gun, she's going to put her hand on it because, guess what, you taught her to put her hand on it."
Police have not determined where the photo was taken. The investigation is ongoing.
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