BURLINGTON, N.C. -- According to the Federal Bureau of Investigation, only 22-percent of arson cases are solved. In 2014-2015, there were 63 intentional fires set in Greensboro and only 17 arrests.

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"There's a lot that goes into proving it, there are instances where there may not be a lot of follow up investigation done after or the scene may not be worked for several days after that's part of it but it is difficult to prosecute," said Assistant Special Agent in Charge Reid Sasser, The State Bureau of Investigation.

Assistant Special Agent in Charge Sasser is an Arson Coordinator for The SBI. Each year, the SBI works on hundreds of fire investigations. When working an arson case, K9s play an invaluable role.

The K9s able to sniff out accelerants used and lead investigators to the source of the fire.

"They're invaluable. We use them a lot. We have a number of dogs across the state and they're excellent in pinpointing areas of evidence," said Assistant Special Agent in Charge Sasser.

Investigators like Sasser then dig out the scene and send any evidence to a lab to be tested.

"The key to getting a conviction is conducting a thorough fire scene examination, documenting the scene, collecting of the evidence and the continual investigation of conducting the interviews and following up on all the leads until there are no more."

Tuesday, hundreds of fire investigators from across the state met in Burlington for an annual arson conference. Investigators are learning new tools and practices to help solve these cases. But for even the most well trained investigators, there are still have problems.

Physical evidence can be destroyed in the fire and often witnesses don't notice the flames until the arsonists is long gone. Rockingham County Fire Marshal Robert Cardwell knows the frustration arson cases carry. There are three unsolved church arsons in Rockingham County.

"You look at a normal crime such as a break-in or a homicide, there's a lot of physical evidence. And unfortunately with fires, that physically evidence is burned up," said Fire Marshal Robert Cardwell, Rockingham County.

He added, "We've got good suspects but we just have absolutely no proof to work with."

There is no statute of limitations on felony arson cases in North Carolina. That means someone could be prosecuted for a fire intentionally set decades ago.

READ: State Law: Arson and Other Burnings