Donell Harvin, a homeland security and public health emergency expert at Georgetown University, told CNN on Sunday that the attacker may have conducted pre-operational surveillance and come up with a plan that maximizes fatalities and damage.

“This looks like a relatively new type of what we call hybrid threat where not only you’re vehicle-ramming to maybe get some chaos but you’re also shooting into a crowd—and may have, it seems, potentially started the fire,” he added.

According to local law enforcement, the suspect crashed a pickup truck through the front door of the church, then got out of the vehicle and started shooting with an assault rifle.

Minutes later, police arrived on the scene and shot the man, who died and was later identified as Thomas Jacob Sanford, a 40-year-old from the nearby city of Burton.

The church was also set on fire, and U.S. law enforcement officials told NBC News that as many as three improvised devices were found at the scene. Michigan State Police bomb squad also responded to the attack.

“That all creates chaos,” Harvin told CNN. “It could create what we call a fatal funnel trying to drive people towards one location.”

According to the New York Post, Sanford was a Marine Corps veteran who had served in Iraq. Police have not yet determined a motive or if he was connected to the church.

So far, at least two people have died from the attack, excluding Sanford, and several more are injured. Police said hundreds of people were in the church at the time.

It was the latest attack on houses of worship recently. Earlier this month, a suspect set fire to a synagogue in Florida. In August, two children were killed during Mass at the Church of the Annunciation in Minneapolis. In July, two women were fatally shot at a church in Lexington, Ky.

“PRAY for the victims, and their families. THIS EPIDEMIC OF VIOLENCE IN OUR COUNTRY MUST END, IMMEDIATELY!” Trump wrote on social media on Sunday.