(CNN) - The debit card used to purchase the 2-gallon gas cans hours before the first Louisiana church burned down bore the full name of the suspect -- Holden James Matthews, according to a court affidavit.
State and federal investigators obtained surveillance photos of the man who -- along with the Scepter-branded gas cans -- also purchased a 10-pack of automotive cloths and a lighter at a Walmart in St. Landry Parish. The cashier recorded the 21-year-old's birthdate on the receipt, the affidavit said.
A piece of a charred gas can was discovered at one of three historically black churches in rural St. Landry Parish, west of Baton Rouge, that investigators said were intentionally torched over a 10-day span, according to the affidavit.
When investigators learned that Walmart was among the sellers of Scepter gas cans, they asked the retailer to check recent purchases -- and that's how they came across details of the March 25 buy at the St. Landry Parish store, the affidavit says.
Matthews left a long list of other clues, investigators say
Not much is known at this time about Matthews. He is the son of a St. Landry Parish sheriff's deputy and may have been influenced by "black metal" music and its "associated history with church burnings," State Fire Marshal H. "Butch" Browning said. But Matthews left a long trail of clues that ultimately led to his arrest Wednesday.
"We are extremely, unequivocally confident that we have the person who is responsible for these tragic crimes," Browning said.
A pickup believed to have been driven by Matthews was captured by surveillance cameras leaving the parking lot of Greater Union Baptist Church moments before it went up in flames April 2.
The affidavit said the pickup was later captured driving by the fire scene and stopping in front of the church. A firefighter also reported seeing the pickup near the burning church, the affidavit said.
A Walmart surveillance photo showed Matthews in a similar pickup outside the store. The Walmart purchase was made late on March 25, less than three hours before the first blaze. A Ford pickup such as the one Matthews was seen driving was registered to his father, Roy. The suspect's cell phone was traced to the area of the fires, the affidavit said.
"This case was solved with boots on the ground and butts in the air," said St. Landry Parish Sheriff Bobby Guidroz, adding that Roy Matthews helped direct his son away from his home to facilitate the arrest.
The motive for the fires is still under investigation, and federal officials are looking into whether a hate crime was committed. Matthews is charged with three counts of simple arson on a religious building.
"Information investigators have uncovered, and that Matthews has offered, suggests a possible connection with a genre of music called 'black metal' and its associated history with church burnings in other parts of the world -- which have been documented in movies and books," Browning said.
Pressed on the possible "black metal" link, Browning said: "We believe there is a relation there with that. That is still being vetted. ... That is a piece that we're looking at."
Investigators examine his Facebook posts on music and Nordic religion
Matthews was active in Facebook groups that focused on black metal and heathenism and Nordic religious beliefs, according to posts seen by CNN. In one post he wrote of his Asatru beliefs, which center around Norse gods.
In two Facebook posts in October, he appeared to admit he illegally carries a handgun -- in addition to a knife and dagger.
"I carry this," he wrote with the photo of a handgun. "Maybe not legally but I only truly follow the law of Odin..... which says as you said, arm yourself."
On the day that authorities said Matthews allegedly set fire to Greater Union Baptist Church in Opelousas, he wrote, "I'll take Arson/assassin/bard" when a group member asked people to choose between a wizard, fighter, sniper, assassin, guardian and warrior.
The suspect's father -- a sheriff's deputy -- was heartbroken, sheriff says
Guidroz, the sheriff, spoke of the difficulty of informing deputy Roy Matthews about his son. The deputy broke down.
"I love Roy Matthews," Guidroz said. "Roy Matthews is one of my best friends. A great deputy. He knew nothing, nothing about his son's activity."
Guidroz said the elder Matthews, shocked and heartbroken after being told his son was a prime suspect, arranged for his son to leave the house and go to a location where he was arrested without incident.
Asked about the suspect being the son of his deputy, Guidroz said: "That's tough. That should tell the country that no matter who you are, there are consequences to the things that you do."