Then he walked into the store, pulled out a "normal-sized knife" and demanded cash.
The other customers slowly moved away, Nazir recalled, and then he told the suspect, "No."
"I said, 'Man, I'm not going to do that.' "
When the man repeated his demand for money, Nazir pulled out his gun.
Nazir declined to describe his gun in detail, but said it is a .45-caliber handgun.
When the suspect saw the firearm he placed his knife on the counter and slowly walked out of the store, heading east on 3900 South toward State Street. Moments later, police responding to a 911 call located the suspect inside a nearby Kentucky Fried Chicken outlet and took him into custody without incident.
The 28-year-old Mexican national was booked into Salt Lake County jail on suspicion of aggravated robbery, a first-degree felony. He was being held without bail on Tuesday.
Nazir said he's glad he had the gun, which he alone has access to at the store. He also said the store has been burglarized while it was closed, and this is was the first time he has had to brandish his weapon at a would-be robber.
"I have a right to protect myself," he added. "If you use it right and you use it sensibly, there is nothing wrong with a gun."
Keller declined to comment on the wisdom of brandishing a gun at a potential criminal, but said that the incident ultimately "did go well, no shots were fired."
Keller also pointed out that Nazir was able to protect his own life, as well as the lives of his customers, because he had the gun.
Still, Keller described owning a gun as "a lot of responsibility," which requires training, among other things. Keller added that the use of deadly force is only legal when protecting life and not when protecting property.