A 14-year-old was arrested Monday in connection with a convenience store shooting in Garland, Texas, that left three people dead and one in critical condition, Garland Police Chief Jeff Bryan said during a news conference.

The three victims from the Sunday shooting were all teenage boys from Garland, Bryan said. They were identified Monday as Xavier Gonzalez, 14, Ivan Noyala, 16, and Rafael Garcia, 17, according to anews releasefrom Garland Police. A 15-year-old boy was taken to the hospital and is stable, the release said.

During the news conference, police played video from the scene that showed the outside of the store. In the video, a person wearing shorts and no shirt opened the door to the store and began shooting.

"The gun used in this incident was a 40-caliber pistol. It had an extended magazine," Bryan said. "We know he fired at least 20 rounds because we found the shell casings."

Bryan added that police are working to determine a motive. "'Why' is one of our big questions right now," he said.

Police are also looking for a person of interest in the case and a white pick-up truck.

"There is a second person that we're looking for," Bryan said. "Right now, we don't know who he is ... He is not suspected of the shooting, but he is a person of interest that we want to talk to."

Garland is part of the north Texas "Metroplex," just northeast of Dallas. (Text excludes headline from CNN)

•Video from a convenience store in Garland, Texas, where a deadly shooting took place Sunday, December 26, 2021