Police have description of Ohio highway shooter
Two vehicles fired on near Columbus over the weekend
Traffic is backed up for miles on I-71 Sunday after the two shootings.
(CNN) -- Investigators trying to solve a string of highway shootings near Columbus, Ohio, now have a description of the shooter who fired on two vehicles a day earlier.
The shootings are the latest incidents authorities believed are linked to a string of 21 others southwest of the city since May, including one that was fatal.
A passenger in one of the cars attacked Sunday described the shooter as a white male, between 30 and 40 years old, in a small dark car, Franklin County Sheriff Chief Deputy Steve Martin said Sunday. The witness also said the man held a handgun as he stood on the overpass bridge and fired down at the vehicle.
No one was injured in either of Sunday's shootings, which happened minutes apart at two interstate overpasses about a mile from each other at 11:20 a.m. ET, Martin said. In each case, a bullet struck the driver's-side hood of vehicles traveling northbound on Interstate 71 southwest of Columbus.
The first vehicle hit was a white minivan and the second was a brown Mercedes.
"We've seen this guy, so we have witnesses that saw him," Martin said. "Can they make an eyeball description of him? Probably not, but at least he's been seen."
All 21 shootings have been linked, most through ballistics tests. Martin said investigators with the Columbus police crime lab are examining Sunday's evidence.
No one was injured Sunday, but the two attacks -- minutes apart in broad daylight -- suggest the shooter is "pretty brazen," Martin said.
The shootings took place on two different bridges over Interstate 71 in Fayette County, about 35 miles from the intersection of Interstate 71 and Interstate 270, the Columbus beltway. The locations are farther south than any previous shootings.
Martin, whose department is the lead agency in the task force probing the shootings, appealed to motorists along I-71 to the south be on increased alert.
State and county law enforcement agencies increased "overt and covert" patrols in the area, he said.
Since May, there have been 21 shootings on or near the southwest corridor of Interstate 270, which circles Columbus. A woman was killed November 25 when she was shot as she rode in a car on that highway. No other injuries have been reported.
There is a $60,000 reward for information leading to the arrest and indictment of whoever is responsible.
Last month Martin told reporters that a caller to the Franklin County Sheriff's Office claimed to be the person shooting at cars. He refused to give details about the call.