A gunman opened fire Sunday night in downtown St. Louis near Busch Stadium, killing one and injuring another, local reports said.

Authorities did not release a description of the gunman. One victim was hit in the head and was unresponsive when authorties arrived and the other was hit in the leg. Authorities did not identify which victim died, KSDK.com reported.

Authorities said both victims are being treated at the hospital. The victim who was shot in the head was listed in critical, unstable condition, The St. Louis Post-Dispatch reported.

The report said there was a “chill” event at the Budweiser Brew House at Ballpark Village. The event was tickets and invite-only. An argument broke out at about 8 p.m. The report said the two people struck were believed to be innocent bystanders.

Maj. Mary Warnecke, from the St. Louis police, said several hundred were at the rooftop event, which was reportedly organized on Facebook.

“We have lots of security at venues like this, but if someone pulls out their weapon…it’s very difficult to prevent.”