The city’s fire marshal has called last week’s fire at the former Dickson County Ambulance Service building “suspicious” and the Dickson Police Department has joined the investigation. Dickson County also has hired a private specialist to assist the investigation. Investigators were back in the West End Avenue building Thursday morning searching the gutted interior for clues. In an email, Dickson Fire Department Fire Marshal Robby Street said, “at this time it is being considered suspicious only.” Street confirmed that Jimmy Jennings, a former Dickson firefighter who is president and chief investigator for Origin and Cause Investigative Resources, has been brought in to assist in the investigation. A former member of the Dickson City Council who now is a captain with the Franklin Fire Department, Jennings is a certified fire investigator through the International Association of Arson Investigators. Det. Chad Fussell of the Dickson Police Department’s Criminal Investigations Division also was on the scene Thursday morning and confirmed the department has opened an investigation. But Fussell and Street said they could not comment any further while their investigation is ongoing. County Mayor Bob Rial said in an email that the building is believed to be a total loss from the early morning fire that gutted the interior and consumed most of the roof on the block building. The county has been using the building for storage and was in the process of remodeling it for offices for its facilities maintenance department and a backup Emergency Operations Center. Rial said that process was about 75 percent complete at the time of the fire. The mayor said the fire is believed to have started in an area of the building that was not part of the remodeling project, but investigators would not confirm that.