A suspect in custody in connection with fires at three historically black churches in Louisiana was identified Thursday morning as Holden Matthews, 21, the son of a local sheriff's deputy, a source briefed on the investigation told NBC News.

Federal prosecutors confirmed the arrest Wednesday night and said the suspect was in state custody, but did not name him.

The fires have broken out at the three historically African American churches in St. Landry Parish since late March.

"The U.S. Attorney’s Office, ATF, and FBI are working with state and local law enforcement and stand shoulder-to-shoulder with the victims and those St. Landry Parish residents affected by these despicable acts," U.S. Attorney for the Western District of Louisiana David C. Joseph said in a statement.

The statement does not indicate a suspected motive.

ABC station KATC of Lafayette first reported that a suspect was in custody, citing law enforcement sources.

There have been no injuries in the blazes, which were reported at the St. Mary Baptist Church in Port Barre on March 26, the Greater Union Baptist Church in Opelousas on April 2, and the Mount Pleasant Baptist Church in Opelousas on April 4, officials have said.

Port Barre is around 11 miles east of Opelousas.

The churches were empty at the time of the fires, officials said, and each suffered considerable damage, forcing worshippers to hold Sunday services at other locations.

A fourth fire last weekend at a church with a predominantly white congregation in another parish 200 miles away doesn't appear to be connected, authorities have said.

A news conference is expected in St. Landry Parish on Thursday morning, in which Gov. John Bel Edwards, the state fire marshal, and other federal and state law enforcement officials are expected to attend. They will provide an update "on the fires that burned three historically African-American churches in St. Landry Parish over the span of 10 days," Edwards' office said in a statement.

About 200 people, including from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives, had been examining the latest cases in Louisiana to help determine whether the fires were intentionally set and may have been motivated by racism or extremism.

After the third fire, State Fire Marshal Butch Browning told reporters that investigators had identified "suspicious elements" in each case and "believe that crimes have occurred."

Derrick Johnson, president and CEO of the NAACP, said in a statement earlier this week that "the spike in church burnings in Southern states is a reflection of the emboldened racial rhetoric and tension spreading across the country."