Dozens of vacant homes have been set ablaze since a pre-Halloween arson spree last week, causing hundreds of thousands of dollars in damage.

Late Wednesday and early Thursday, four fires erupted on the same block in this city of about 60,000 residents, causing more than $70,000 in damage. No one was injured.

"Why would anybody keep doing this?" Battalion Chief Donald Coleman asked.

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Firefighters have battled more than 50 fires since the Oct. 30 spree in which 16 houses, most of them vacant, burned. Since then, homes, cars and garbage have been set ablaze.

Widespread arson fires on the night before the Halloween holiday, dubbed Devil's Night, started years ago in Detroit. Saginaw later began seeing copycat arsons.

Police have said a police officer trained in arson investigation will be working with Fire Marshal Gregory Barton to sift through charred homes, interview potential witnesses and track down leads.

"I would think the criminals would be a little less inclined to burn things down if they think they might be caught," Police Chief Gerald H. Cliff said.

Detroit has nearly eliminated Devil's Night arsons thanks to a neighborhood patrol movement involving tens of thousands of volunteers that began in 1994.