DETROIT — The man who attacked Grand Blanc Township churchgoers last month, leaving four dead, was acting on anti-Mormon beliefs, federal authorities announced Friday.

"Based upon the facts, circumstances and information obtained in this case, I am confirming that this is a targeted act of violence believed to be motivated by the assailant's anti-religious beliefs against the Mormon religious community," Jennifer Runyan, special agent in charge of the FBI's Detroit Field Office, said in a video statement.

Runyan did not explain how investigators arrived at their conclusion, noting that federal Department of Justice policies prohibit the FBI from providing details regarding investigators' specific actions and techniques.

"This motivation was determined based upon countless hours of investigative efforts by our team, as well as the cooperation of law enforcement partners, the community and the U.S. Attorney's Office for the Eastern District of Michigan," Runyan said in the statement.

On the morning of Sept. 28, Thomas "Jake" Sanford of Burton allegedly set fire to the Latter-day Saints church building on McCandlish Road in Grand Blanc. Police say he also fired several rounds, striking 10 people.

Two people died from gunshots and two bodies were found in the rubble left by the blaze. Sanford was shot and killed by law enforcement officers after they arrived on the scene.

In addition to the fatalities, nine people were injured in the attack, Runyan said.

Sanford, 40, was a former U.S. Marine who served in Operation Iraqi Freedom. One Burton resident who had previously met Sanford told reporters that the assailant had shared with him anti-Mormon sentiments, including saying that "Mormons are the Antichrist."

Runyan said the FBI's investigation is ongoing with partners including the Grand Blanc Township Police Department, the Genesee County Sheriff's Office, the Michigan State Police and other state and federal agencies.

More than 100 FBI personnel have been involved in the probe, she said.

"On behalf of the FBI Detroit Field Office. I would like the entire Grand Blanc community to know that we stand with you," Runyan said.

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