Investigators suspect three fires at black churches in southern Louisiana over just 10 days are "related".
Federal authorities have joined the inquiry into the fires, which occurred on 26 March, 2 April and 4 April in the St Landry Parish.
Officials have not yet determined the cause of the blazes, which did not result in deaths or injuries.
But the fires have dredged up painful memories of how black churches were razed back in the US civil rights era.
"Right now, what we have to say is that the fires are suspicious," said Louisiana State Fire Marshal Butch Browning, reports NBC.
"We do believe that crimes have occurred. We believe that the three fires obviously are not coincidental, they are related."
The fires engulfed St Mary Baptist Church, the Greater Union Baptist Church and the Mount Pleasant Baptist Church, all in the same rural community 30 minutes north of Lafayette.
The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives have joined the investigation.