sam richardson never even entered the garage. >> so you think this was fire investigation 101? investigation 101. this is -- >> reporter: but the sloan case isn't the only one? just six days prior, richardson and andies had been called to another house fire across town. >> there is three separate points of origin here on the back patio. >> richardson made up his mind on the scene. >> so this will be an arson fire with a possible suspect. >> reporter: the suspect was a former sheriff's deputy and renter of the house. he was behind on his rent and had been fighting with his roommate. >> he wasn't paying rent. he came back. they wouldn't let him in. he got mad. and saw him just prior to the fire. >> part of the suspicion was that you were freeing to kill your roommate? >> correct. >> reporter: any truth at all to that? >> none at all. >> reporter: richardson using his new training took on the role of interrogator. >> i know you lit the fire. let me tell you why. okay. i got a good video of you coming back. a good eyewitness that saw you back there just prior to the fire. >> reporte

. >> reporter: this is captain sam richardson. >> two fires today already. >> reporter: and captain fred wrap. >> reporter: they're investigators with phoenix's elite 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 didn't commit. >> reporter: barbara sloan and carl caples, a former sheriff's deputy, claim they were falsely accused of arson. >> you were in jail for 16 months? >> it ruined my life. >> reporter: adding credibility to their charge, the findings of an arson investigator hired by the defense. >> i think there are other cases, other innocent victims out there. >> reporter: nearly five years ago abc news was given extraordinary access to this elite unit, an inside look at what made them the best in the nation. >> sadie is an accelerant detection canine. she's a food reward dog. >> reporter: the unit is run by a charismatic and confident former police detective, jack valentine, who by his own admission had no prior background in fire investigations. under h