Police Sgt. Candice Jones stepped from the East Side sunshine into the darkened law office. A thin film of soot covered every surface, from the ceilings to the floors. A strong smell of smoke hung in the air. Near the back, a basement stairwell ceiling was heavily charred, indicating that the fire began in the lowest level of the two-story brick building.

To Jones, also a St. Paul arson investigator, it was clear that this fire was deliberately set. “There is evidence of accelerant,” she said. “And there are multiple points of origin.”

Jones inspected the burned-out office Tuesday afternoon, along with Joe Blank, a fire department investigator, to begin piecing together the clues that may help them figure out who set the fire. Thanks to Jones and Blank and their interdisciplinary team of arson-fighters, investigators in St. Paul have been hugely successful over the past five years in reducing the number of arson fires and sending more arsonists to prison.

On Wednesday, the St. Paul Fire Department honored Jones, three full-time fire investigators, a Ramsey County prosecutor and several other team members for their work. Arson numbers are down 48 percent since 2007 and 17 percent in the last two years. At the same time, arson arrests are up 41 percent, and arson prosecutions have tripled since 2008.

“This amazing team has seen amazing results,” said St. Paul Fire Chief Tim Butler.

Jones, who joined the unit in September 2011 and works out of Fire Station No. 1, said the results come from coordinating the investigative work.

Fire investigation team leader Jamie Novak and fire investigators Brian Kroeger and Blank determine the cause of every blaze. If a fire is suspicious, they call Jones. Once they have identified a suspect, they begin working with Assistant Ramsey County Attorney Sarah Cory — who has received special training from the fire department — to build as strong a case as possible.

The unit is working on close to 30 cases, Jones said. All are challenging.

“Arsons are probably the hardest cases to solve,” she said, noting that the crime often occurs at night with no witnesses. Fire also can destroy evidence.

Still, she said, the team has had many successes — including winning a conviction for a fire at St. Mark’s Lutheran Church on W. Seventh Street two weeks before Christmas.

Investigators had suspected a 27-year-old man of setting other fires in the area. He had been a regular presence at St. Mark’s — the church sometimes fed him and counseled him — and there had been a falling out.

Although there were no witnesses, investigators scoured the scene and canvassed the neighborhood for evidence that led to the man’s arrest on a Friday. A weekend of intense work by investigators and Cory led to charges the following Monday. The man later pleaded guilty to setting the fire.

St. Paul Mayor Chris Coleman on Wednesday praised the arson investigative team. Arson, he said, destroys trust in a community and damages residents’ sense of belonging. The fire at St. Mark’s, he said, caused “a real sense of betrayal and broken trust.”

The unit’s work has done much, Coleman said, to “rebuild trust and rebuild the faith that we have.”