Dulcogas, from the makers of Dulcolax- Nothing relieves gas faster. Nearly 17,000 fires across America are intentionally set, but arrests are made in only about 20% of those arson cases, except in... See More
Dulcogas, from the makers of Dulcolax- Nothing relieves gas faster. Nearly 17,000 fires across America are intentionally set, but arrests are made in only about 20% of those arson cases, except in Phoenix. Long considered the best in the country, the city's elite arson squad is finding itself under fire. An ABC news "Nightline" investigation is looking into how the team racked up its impressive arrest record. Reporter: This is captain Sam Richardson. Two fires today already. Reporter: And captain Fred Anderson. They're investigators with Phoenix's arson squad. They threw something in here. Reporter: Critics asking did that success come at the expense of innocent victims. I was being framed for a crime that I didndidn't commit. Reporter: These women claim they were falsely excused of arson. You were in jail for 16 months? It ruined my life. Reporter: The findings of an arson investigator was hired by the defense. I think there are other cases, other innocent victims out there. Reporter: Nearly five years ago ABC news was given access to this elite unit, an inside look at what made them the best in the nation. Accelerant detection canine. Reporter: The unit is run by a charismatic and confident police detective, jack Valentine who by his own admission had no prior background in fire investigations. The unit's clearance rate skyrocketed from solving 22% of the cases in 2007 to 65% in 2010, the highest in the country. Back then the team was proud to boast about their success. Not now. Can we talk to you about the investigation? I take the the answer is. We used to think that we had to have concrete evidence and often we do. But now we've gotten smart enough where we can put a case together with circumstantial evidence and make it stick. Charges were eventually dropped. Barbara Sloan believed she was falsely accused to boost the Numbers. I believe he was pushing for the arson rate to be the best in the nation. The case is under review by the Phoenix public safety office. Results are due back in the coming weeks.
This transcript has been automatically generated and may not be 100% accurate.