(Adds detail on spill cause and estimate on volume)
May 3 (Reuters) - A black sheen discovered in a storm drain in southeastern Michigan on Thursday was most likely the result of motor oil dumping and was not a crude oil spill, local police said.
Lieutenant Luke Riley of the Sterling Heights police department said the spill was contained by booms in the Red Run drain, which leads into the nearby Clinton River near Warren, about 20 miles north of Detroit
Warren Mayor James Fouts said the spill was estimated at 50 gallons of oil-based product.
Police and fire departments were investigating to determine if the spill was intentional and if criminal charges would be sought.
(Reporting by Edward McAllister in New York, Bernie Woodall in Detroit, David Sheppard in London and Naveen Arul in Bangalore; editing by John Wallace)