An ex-Marine smashed a pickup into a Church of Jesus Christ of Latter-day Saints church in Michigan, opened fire and set the building ablaze during a crowded Sunday service and then was fatally shot by police. At least four people were killed and eight wounded, and authorities were searching the building ruins for more victims.

The attack occurred about 10:25 a.m. while hundreds of people were in the building in Grand Blanc Township, outside Flint.

The man got out of the pickup with two American flags raised in the truck bed and started shooting, Police Chief William Renye told reporters. The attacker apparently used gas to start the fire and also had explosive devices but it wasn’t clear if he used them, said James Dier of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Authorities identified the shooter as Thomas Jacob Sanford, 40, of the neighboring small town of Burton. The FBI is leading the investigation and considered it an “act of targeted violence,” said Ruben Coleman, a special agent in charge for the bureau.

Officers responding to a 911 call were at the church within 30 seconds, Renye said. After the suspect left the church, two officers pursued him and “engaged in gunfire,” killing him about eight minutes later, the chief said.

People inside the church shielded children and moved them to safety during the attack, Renye said.

Flames and smoke poured from the large church for hours before the blaze was extinguished.

Two bodies were found during a search of the debris, and Renye said more victims could be found as searchers made their way though the entire church. One of the wounded people was in critical condition Sunday evening and the seven others were stable.

Renye said “some” people were unaccounted for, but he didn’t have an exact number.