Surveillance video shows the three suspects enter the store with their faces covered.
The first one has a long gun. Two others follow, and they immediately ambush a clerk.
A manager can be seen handing over the cash register.
Two customers seen on the video came into the store while the robbery was in progress.
The manager told FOX 4 that whichever crook was supposed to watch the door didn't bother to lock it.
Meanwhile, in the back room, things turned violent when the crooks wanted to get into the safe. Police say they forced an employee to open the safe and hit him in the head with a pistol.
Anyone with information on the crime or suspects is asked to call Crime Stoppers at (214) 373-TIPS or contact Investigator D. R. Phillips at 972-216-8153.
Crime Stoppers is offering a reward of up to $5,000 for information called into Crime Stoppers that leads to an arrest and indictment.