Police took 22 complaints Oct. 16-18 of motorists being shot at across five neighboring towns between Ann Arbor and Detroit.
Oakland County Undersheriff Michael McCabe said bullet fragments analyzed from seven of the shootings are all from the same gun.
"We can't say with certainty what caliber weapon they came from at this point," McCabe told The Detroit News Wednesday. "But seven of these incidents are from the same weapon."
Most of the shootings came on Interstate 96, and police said they have received hundreds of tips about suspicious people or vehicles in the area. The FBI and federal Bureau of Alcohol, Tobacco, Firearms and Explosives have offered an $11,000 reward for information leading to the suspect's arrest.
The heaviest concentration of attacks have been reported in Wixom, Mich., where 10 people reported being shot at, police said.