At first, investigators thought the succession of suspicious fires in abandoned buildings south of Boston might not be connected, because they broke out over such a large swath of suburbs.
But when they kept recovering remnants of fire-starter logs from the scenes, they realized they were dealing with serial arson. That discovery spurred what the state’s fire marshal is calling the largest arson investigation in recent memory, which on Thursday led to prosecutors filing charges against a Middleborough man and his stepson.
Mark Sargent, 45, is accused of setting fire to an unfinished building in West Bridgewater and is suspected of setting two dozen other fires in the region since last fall. They also charged his stepson, Jeanmarie Louis, with the West Bridgewater arson, and said they were probing the extent of his involvement in the other fires.
A spokeswoman for the Plymouth County district attorney’s office, which is prosecuting the case, could not be reached for comment. A lawyer for Sargent declined to comment, while a lawyer for Louis said he is contesting the charges.
After Sargent’s arrest Wednesday night, police went to search his home and were admitted by his girlfriend, Myrna Antoine. While they were searching the bedroom, she shouted at police while holding a metal skull, then allegedly attacked two police officers with a machete, said Joe Perkins of the Middleborough Police Department.
Antoine brandished the machete “in a menacing way,” Perkins said. She shouted that she was from Haiti and could “do voodoo,” he said.
There was evidence that Antoine had been drinking, Perkins said.
After a brief standoff, she was arrested and charged with two counts of assault. Antoine’s two children, ages 2 and 13, were removed from the home and are in state custody.
Details about Sargent’s life were scarce.
Randy Gould, a neighbor of Sargent for the past two years, said he rarely interacted with other residents.
“It seems like he’s always gone,” he said. Each year around July 4, however, Sargent would host an elaborate fireworks display in a lot beside his house.
“It would go on for two, three hours,” Gould said. “He would light up $1,000 a night easy.”
Gould said he saw no signs of erratic behavior in Sargent, and was stunned by the accusations against him.
“You hear this stuff on the news, but not about your neighbor,” he said.
Authorities have not disclosed any motive for the arsons, but Sargent’s arrest was met with widespread relief among area fire officials.
“It’s been a concern of every firefighter in the region,” said George Rogers, chief of the Fire Department in Bridgewater. “Now we can all rest easier.”
Stephen A. Coan, the state’s fire marshal, said that six firefighters sustained minor injuries responding to the string of fires and that blazes in vacant and abandoned buildings are often highly dangerous.
“Firefighters are far more apt to be injured” responding to fires at these buildings, he said. “The buildings are often in disrepair.”
Police first stopped Sargent shortly after midnight Dec. 20, shortly after fires broke out on three boats at a Marshfield boatyard.
Sitting in his car nearby, Sargent appeared nervous and told police he was “just driving around’’ the area, prosecutors said.
Police quickly obtained a court order to attach a GPS tracking device to his car, then monitored his vehicle as it was driven near seven arsons at the times the fires broke out, authorities said.
They also discovered that Louis used his credit card at a convenience store in Halifax on the same day an intentionally set fire damaged a building in that town.Peter Schworm can be reached at email@example.com. Follow him on Twitter @globepete.