For the second day in a row, an unidentified gunman fired shots near Camp Shelby Joint Forces Training Center, a military outpost in Hattiesburg, Mississippi. State investigators have a suspect in custody, the Associated Press reports.

Around 11:45 a.m. on Tuesday morning, soldiers near a checkpoint reported that a firearm was discharged from a red pickup truck on a road outside of the base’s perimeter. At 8 a.m on Wednesday, shots were again fired from the same area, from what appeared to be the same red pickup truck, authorities said. No soldiers were injured in either case.

“We’re currently working with the Perry County Sheriff’s Office and the Mississippi Highway Patrol to determine who is responsible for this and why it’s happening,” Lt. Col. Christian Patterson, the director of public affairs for the Mississippi National Guard, tells The Trace. “We’re at a high state of alert.”

Camp Shelby is a headquarters for “Jade Helm 15,” a controversial military-training exercise spanning several states, the Army Times reports. The exercise involves more than 1,200 troops, many of them special forces, and runs through mid-August. There are no “operational units” at Camp Shelby, a Secretary of Defense public affairs officer tells The Trace.

Conspiracy theorists allege that the Jade Helm could result in martial law or mass gun confiscation — causing some to bury their guns, or stockpile ammunition and attempt to build homemade explosives. Texas Gov. Greg Abbott ordered the Texas State Guard to watch Jade Helm’s activities.

In response to last month’s attack on two military installations in Chattanooga, Tennessee, all the entrances at Camp Shelby are patrolled by armed guards. Currently, the facility is hosting a summer training exercise that is not part of Jade Helm, involving over 4,500 active-duty soldiers.

“They’re a resilient force,” Patterson says. “And at the moment, they are continuing with their exercises.” According to him, the base hasn’t received any direct threats. But, he says, “There a lot of unanswered questions.”

[Photo: (AP Photo/The Hattiesburg American, Matt Bush)]