No one has been hurt, and no shootings have occurred since Thursday. But police on Monday added to their list two more incidents from the small city of Perry, off U.S. 69, stretching the investigation to four counties, Oakland County Undersheriff Mike McCabe said.
Tipsters told police the gunman appears to be a man in his 30s and authorities on Sunday released a drawing of a possible suspect with close-cropped hair and stubble on his cheeks and chin. While the incidents appear to be random, police are investigating them as a pack and have formed a task force to chase down tips.
The shootings mostly involve cars near Interstate 96, though authorities have said one occurred while a man was taking out his garbage. In another incident, a woman said the rear window on her car was shattered. Ten of the 20 shootings have occurred in Wixom, 35 miles northwest of Detroit.
In the Walled Lake district, officials felt compelled to lock doors at five schools in Wixom and hold recess indoors on a beautiful fall day, though there is no evidence schools are a target. They're not sure how long the policy will be in effect.
"We want all our students and families to feel safe. These are precautionary measures," school spokeswoman Judy Evola said.
The shootings were a hot topic on morning drive-time radio shows with listeners calling or texting their plans to avoid I-96 in certain areas.
"You can never be too careful, obviously," McCabe said. "Until this guy or suspects are found, people need to be aware of their surroundings. There is nothing wrong with taking precautions. We're not going to tell people they're overreacting."
The shootings have occurred in Oakland, Livingston, Ingham and Shiawassee counties, from last Tuesday through Thursday.
Ed White in Detroit contributed to this report.