While investigators were still exploring motives, Browning said that Matthews had "a relationship with a type of music called black metal," an extreme subgenre of heavy metal. Black metal has an association with church burnings in other parts of the world, he said.

https://www.aol.com/article/news/2019/04/11/son-of-sheriffs-deputy-charged-with-burning-three-louisiana-black-churches/23710536/