OPELOUSAS, La. — Much of Monica Harris’s identity is tied to the Greater Union Baptist Church, a 129-year-old sanctuary that has been at the center of her family for generations. As a child, she was dunked into a baptismal basin and then paraded like a princess up the aisle in a white dress and white patent leather shoes. She was married at the church, and she said goodbye to her parents there, too.

And so she felt like a piece of her was missing when she set eyes upon the charred remains of Greater Union, one of three predominantly black churches in St. Landry Parish, La., that law enforcement authorities said were set ablaze and destroyed over the stretch of 10 days.

“Seeing the church in the condition it is now,” Ms. Harris, 57, said of the tan brick sanctuary where her parents raised their 12 children and where they celebrated dozens of weddings, funerals and Bible studies, “it’s almost like losing a family member.”

It was still not known Monday whether the fires were intentionally set or whether they were motivated by racism. Still, they have drawn the attention of the Bureau of Alcohol, Tobacco, Firearms and Explosives and the F.B.I., which are assisting the Louisiana state fire marshal. The authorities said Monday that they were vetting new information every hour and that an A.T.F. crane had arrived at one of the churches to help process the scene.