A task force comprised of local and state fire investigators unanimously determined that the August 11 fire at Gorve Townhomes was an arson.
Investigators described the 2-alarm fire as a "catastrophic fire event."
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There is no known motive for the arson, but investigators said the case remains under investigation.
Durham Police Department has now launched a formal criminal investigation into the case.
Anyone with information is asked to contact the Durham Fire Marshal's Office at 919-560-4242 x19239 or Durham Police Department at 919-560-4935 x29416.