Chicago police said Monday they won't charge a customer with a concealed carry license who shot and killed an armed man during an attempted robbery of a store on the city's southwest side.

Department spokesman Anthony Guglielmi says investigators classified the shooting as self-defense after they reviewed witness statements and surveillance videos from the store and currency exchange.

A masked man walked into a store and currency exchange Saturday evening on the city's southwest side, displayed a handgun and announced a robbery to an employee, Guglielmi said. The gunman then pointed his weapon at another employee and forced her to the back of the store.

The armed customer then shot and killed the man, identified Sunday by the Cook County medical examiner's office as 55-year-old Reginald Gildersleeve. Other details about Gildersleeve weren't released.

Gildersleeve's stepson cast doubt on the police account, the Chicago Tribune reported. "Something doesn't seem right," Igbinosa Oronsaye said, adding, "Reggie doesn't even own a gun. He couldn't own a gun if he wanted to."

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No one else was hurt during the incident.

The incident could add more fuel to the ongoing debate about whether the proliferation of handguns is responsible for crime or if more guns in the hands of law-abiding citizens can actually make people safer.

"It doesn’t get national news attention, but the over 13 million concealed handgun permit holders in the U.S. are getting local news coverage in stopping crime every day," said John Lott, president of the Crime Prevention Research Center."

He cited three recent cases in Detroit, where Police Chief James Craig has encouraged citizens to get gun permits and carry weapons as a means of ensuring public safety. In one, a a 23-year-old permit holder stopped three robbers who threatened to kill him; in another, a 63-year-old man stopped would-be robber after he withdrew money from an ATM; and in a third, a pastor stopped a man from attacking him with a brick.

But also last month, a Michigan woman with a concealed carry license shot at shoplifters fleeing a Detroit-area Home Depot store, flattening a tire of their SUV. No one was hurt, and the suspected shoplifters were arrested several days later. The woman faces up to 90 days in jail after pleading no contest to a charge of reckless discharge of a firearm. Two other shootings in which citizens fired at lawbreakers or potential lawbreakers also happened in September in Michigan.

"It's a slippery slope" when it comes to the question of whether citizens who are licensed to carry guns should intervene in dangerous situations, if at all, Guglielmi said.

"You have situations like this," he said, referring to the foiled Chicago robbery. "And you have situations that end tragically. The department is not going to advocate for what people should or shouldn't do."

The Associated Press contributed to this report.