UPDATE, 9:20 PM: The car may contain explosives, according to WFAA8:
Two men were shot and killed in a parking lot outside the Curtis Culwell Center in Garland Sunday afternoon, SWAT officials told News 8.

The two suspects drove up and opened fire on the center, which was hosting a Muhammad Art exhibit, and hit a Garland ISD officer.

That officer suffered non-life threatening injuries, according to a spokesman for Garland Police.

Police were searching the area for a vehicle that had explosives in it.

SWAT members were already at the scene for the art event.

Rowlett/Sachse Scanner reported on Facebook that a suspect was inside a nearby Walmart, off Garland Avenue and Naaman Forest Boulevard, with a hand grenade.

A 1,000-foot radius around the Walmart was shut down and the Academy Store was evacuated, according to that page.