GARY, Ind. (CBS) — Federal officials are now investigating a suspicious rash of fires in Gary, Indiana.

The fires broke out at several abandoned structures hit by what firefighters believe was an arsonist overnight Saturday into Sunday. A city spokesperson said 15 to 18 structures were burned.

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One fire was at 8th Avenue and Tennessee Street and reignited Sunday morning, still smoldering with the front steps still standing and one wall just barely hanging on.

Another fire was about a half mile away at 8th Avenue and Pennsylvania Street. Crews found another scene 2.5 miles away at 25th Avenue and Washington Street. Then five miles east of those three locations, another fire was ignited at 5th Avenue and Tompkins Street.

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The fire department said all of the structures appear to be abandoned.

Several burned to the ground as the fire department simply could not get to them. The Gary Fire Department was maxed out by the number of fires burning at the same time and had to call in mutual aid from at least 10 neighboring departments.

There were also even more fires three weeks ago.

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The Department of Alcohol, Tobacco, Firearms and Explosives has certified fire investigators in Gary to find out if the flames were set on purpose.

CBS 2 Chicago Staff