OPELOUSAS, La. — While the victims prayed for the soul of the arsonist who burned down their houses of worship, investigators rushed to assemble clues, worried the assailant would strike again.
The detectives had noticed the same pickup truck in surveillance video footage near each of the three predominantly black churches that had been set ablaze and destroyed. They found the charred remains of a particular brand of gas can sold at a local Walmart.
Then the pieces came together, and the authorities announced the arrest of a 21-year-old white man who is the son of a local sheriff’s deputy and an aficionado of a subgenre of heavy metal, called black metal, whose most extreme practitioners in Norway have engaged in church burning, vandalism and killing.
In a Thursday morning news conference announcing the arrest of the man, Holden Matthews, the authorities said that they had not concluded their investigation and could not say whether racism had played a role.
Though the motive was less than clear, the results brought a measure of peace for a rural Cajun community that had been on edge since late March, when the first of the fires occurred.
Monica Harris, a member of the Greater Union Baptist Church, had been uneasy since April 2, when the 129-year-old sanctuary that had been at the center of her family for generations was destroyed. She was baptized and married there, and her parents, who died last year, are buried in the cemetery on the church’s grounds.
“I was uneasy with the fact that somebody invaded their resting space,” Ms. Harris, 57, said on Thursday. “Now that they’ve caught someone, I feel more at ease that they’re able to rest now.”
Gov. John Bel Edwards of Louisiana, speaking of the suspect, said at the news conference that he could not know “what was in his heart.” But he added that it “cannot be justified or rationalized. These were evil acts.”
Mr. Matthews, who did not appear to have a lawyer on Thursday and had no known history of violence or arrests, was charged with three counts of simple arson of a church building. The authorities said the blazes, which occurred between March 26 and April 4, were intentionally set and related. Before Greater Union, there was St. Mary Baptist Church in Port Barre. The last fire was at Mount Pleasant Baptist in Opelousas, the St. Landry Parish seat.
[‘They didn’t burn down our spirit’: Black churches in Louisiana were worried but defiant after the fires.]
A fourth fire, a small blaze that officials said was “intentionally set,” was reported on March 31 at a predominantly white church in Caddo Parish, about a three-hour drive north. State officials said Thursday they did not believe it was related to the attacks in St. Landry Parish.
The arrest of Mr. Matthews came after days of worrying about the community’s remaining churches, and about the fabric of a proud, working-class stretch of Acadiana just north of Lafayette, where the global calling cards are not extreme mutations of heavy metal, but the joyous chug of zydeco or the high lonesome wail of Cajun fiddles.
While no one would characterize the area as a racial utopia, both black and white residents describe it as neighborly. And everyone agrees that churches should be considered inviolable and sacred.
But everyone also knows the story of the South. Since the 1950s, black churches across the region have been the targets of racist attacks, from arson and bombing to armed assault.
The sense of urgency was palpable as the mystery persisted. The F.B.I. and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were involved in the investigation, as well as the Louisiana and Florida state fire marshals, the cybercrime unit of the Louisiana attorney general’s office, and the state and local police.
Social media posts offered a glimpse of the man they arrested.
Facebook photos of Mr. Matthews show a young man with long hair. In one picture, he is wearing a black sleeveless T-shirt and holding a black electric guitar. He described himself as the lead singer of a black metal band called Vodka Vultures, though there was little online evidence of the band’s activity. Still, he wrote several posts that showed his familiarity with the genre.
He wrote favorably of the recent movie “Lords of Chaos,” a dramatized version of the black metal scene, and apparently referenced Varg Vikernes, perhaps the most notorious figure in the black metal movement, who was found guilty in Norway of killing a heavy metal guitarist and burning three churches.
The path to Mr. Matthews was laid out in an affidavit, with the big break coming Tuesday when an A.T.F. team found a piece of what appeared to be a two-gallon red gas can at Mount Pleasant Baptist Church.
The authorities realized that the same can was for sale at a local Walmart. On Wednesday, an investigator working for the retailer shared with them that a similar can had been purchased late on March 25 — less than three hours before the first church fire — along with a package of shop towels and a lighter, all paid for with a debit card that the authorities said was owned by Mr. Matthews.
Investigators learned, too, that Mr. Matthews’s father, Roy Matthews, was a longtime deputy in the St. Landry Parish sheriff’s office and the owner of a beige 2002 Ford pickup that appeared to match the truck that “consistently” appeared “around the time of each fire,” the affidavit states.
Sheriff Bobby Guidroz of St. Landry Parish said that he had summoned Mr. Matthews’s father on Wednesday to tell him that his son was considered a suspect in the fires, which all took place in the middle of the night and did not injure anyone.
“He was shocked and hurt, as any father would be,” Mr. Guidroz said of the older Mr. Matthews, whom he described as “a great deputy” and one of his best friends. “He was in terrible shape.”
At the home where Mr. Matthews lived, a woman declined to comment on Thursday. A horse trailer was parked outside the home, set down a gravel driveway and behind a pond. Farmland filled the distance behind the house, which had few windows.
It was a moment that stood in striking contrast to the news conference, which at times took on the flavor of a tent revival. There was much spirit-infused talk about resilience in the face of hatred — a resilience stronger, and more flame-retardant, than any building.
“I want to say to the individuals who engage in these types of crimes, you have caused pain, and you have caused hurt,” said Dana Nichols, the special agent in charge of the New Orleans office of the A.T.F. “But know this: that you cannot destroy our faith.”
A few pastors called out, “Amen,” and Ms. Nichols went on.
“We can have church anywhere,” said Ms. Nichols, who was raised in the Baptist church in Indiana. “We can have church in a parking lot. We can have church in a field, and as many of us know, when we’re doing our building fund, we can have church under a tent. We can have church on a porch. And know this: We’ll have church in the very parking lot where the building you destroyed will stand as a remembrance to us that God is still with us.”