Norwich - Fire Chief Kenneth Scandariato noticed a problem with arson in the city in 2006 and began tracking the incendiary fires using a map and push pins.
He picked up on certain trends, like fires being reported at 11 p.m. on Tuesdays.
By 2007, there was an arson in the city every two or three weeks.
"I got tired of the taste of charcoal in my mouth, literally," the chief said.
Scandariato also was motivated by the fact that his firefighters were getting injured. He got together with Police Chief Louis Fusaro and the state and local fire marshals, and they formed an arson task force.
Five years later, after a lot of "ground-pounding" investigatory work, Scandariato said, "we are amazed that we've gone 23 (arrests) deep and we are still putting people away."
The latest arrests were earlier this week, when three young men and a 45-year-old woman were charged with setting fire to vacant homes on Oak Street and Lake Avenue on March 26 and March 29.
"Clearly, we have an arson problem, but we're working at it," the fire chief said.
He says the people who are setting the fires seem to be part of a loosely knit group centered downtown. For the most part, they are in the same age group - late teens to mid-20s - and they all know each other.
"These folks who commit the arson know the buildings," Scandariato said. "It's in their neighborhood. They know the buildings are vacant. They know how to get in, get out."
The alleged arsonists broke into the houses and used gasoline and matches to set fire on different levels of both houses, according to court documents.
What's unclear is why they're setting the fires.
One of the accused, Laura MacDonald, a 45-year-old woman who suffers from mental illness, was on probation for setting fire to the Capehart Mill in 2010. Another, 24-year-old Jonathan "Junito" Ortiz, is the brother of Ramon Ortiz, who was also convicted in the Capehart Mill fire.
"It's a social group of people that seem to have a lot of issues," Scandariato said. "They know the area really well. They're picking off these buildings."
Scandariato, a self-described "numbers guy," said he's been in command of 79 fires since he was appointed chief in 2005. Eighteen of them were incendiary. Over the same period, the city has spent more than $500,000 a year on firefighter injuries.
"I've tracked every single bit of it," he said.
Fortunately, incidents of arson or incendiary-type fires seem to be decreasing, the chief said.
"But it's cyclical," he said. "The adage here in the city department is, the longer we go, the worse it's going to get."
He said there has lately been longer stretches between arson fires followed by a small rash of them, "almost as if the people who are doing it can't stand it anymore."
Police Sgt. Christopher Guari, who supervises the state police Fire and Explosion Investigation Unit in eastern Connecticut, said Norwich doesn't stand out except that the arson cases seem to occur in spurts.
"It seems to be a culture where people think it's OK to burn buildings," Guari said. "If you look at the city itself, there's a lot of older homes, abandoned mill complexes, places where people have access."