It happened on Saturday, March 27, at the High Caliber Gun Show inside the Pasadena Convention Center. Authorities say the man was seen walking around with several other people when he was caught stealing the gun.
The incident was captured on video, which was posted onto the Pasadena Police Department's Facebook page.
In the video, you see the suspect wearing a green shirt and face mask walking around with a plastic bag.
You can watch the full video in the video player above.
He is first seen speaking to a vendor and then picks up the handgun. He inspects the gun for a bit while talking to a man in a blue shirt. Shortly after, the suspect is seen putting the gun in the bag and walking away.
Anyone with information is asked to contact Det. E. Dollagaray at 713-475-7889.
RELATED VIDEO: Here are some ways for you to protect your guns