CHICAGO (CBS) — Police are still searching for the gunman who shot and killed a woman caught shoplifting at a Walgreens store in the Belmont Cragin neighborhood, claiming to be an officer, and sources say a clerk at the store had called that man for help.

Around 11:30 p.m. Wednesday, a woman in her 30s was shoplifting at the Walgreens at Cicero and Fullerton, when a clerk confronted her, according to police.

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Police sources told CBS 2’s Brad Edwards the clerk called a friend for help, and the friend showed up at the store with a gun, and intervened as the clerk was confronting the shoplifter.

The gunman then began wrestling with the woman, shot her in the head, and ran away, sources said. The woman was taken to Mount Sinai Hospital, where she was pronounced dead.

According to police radio calls, witnesses said the man who shot her appeared to be a security guard. Witnesses also said the gunman claimed to be a Chicago police officer after he threw the woman to the ground and shot her.

However, police said the man is not an officer. While he might be an unlicensed security guard, the Walgreens does not have any security guards.

Investigators said they have clear surveillance video of the shooter’s face and vehicle, which witnesses described as a Ford Explorer. Police Department spokesman Anthony Guglielmi said police have identified a person of interest wanted for questioning.

The Medical Examiner’s office has not released the victim’s name and age because they are still trying to notify her family.

No one was in custody Thursday morning.

Area Central detectives were investigating.

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A spokesperson for Walgreens said, “We are committed to providing a safe environment for our employees, patients and customers in the communities we serve. We are cooperating with Chicago police in its investigation.”