Police officers combed the rough woods flanking a five-mile stretch of highway encircling the Ohio state capital, where most of the dozen shootings have occurred so far.
But officials had little comfort to offer the panic-stricken residents who drive the designated stretch of Interstate 270, just south of the city.
"I have to use 270 to get to work, but I'm scanning either side of the road the whole time," said Stephanie Genheimer, a 25-year-old shop assistant, who works in Hamilton township, a suburb of Columbus.
Many other locals say they are avoiding the freeway where a 62-year-old grandmother was shot dead on 25 November while driving.
Detectives said her murder was just one of 12 related shootings.
The task force working on the case has linked four of the shootings to the same rifle using ballistic evidence, but believes all 12 are linked.
Authorities have only belatedly begun to piece together the different incidents in part because of a lack of communication between the different police and sheriff's departments who have jurisdiction over the freeway, investigators said.
One of the bullets fired from the gun that killed Gail Knisley was retrieved from a local elementary school, Franklin County Chief Deputy Steve Martin said, in a development that alarmed many parents.
Officers swamped at Hamilton Central School in a reassuring show of force, sweeping school grounds for any additional shell casings with metal detectors.
But 70 students out of 468 were absent, double the norm, according to the school district superintendent Bill Whittman.
Dionna Flaherty kept her four children at home, as many other parents had done.
"I don't feel they're safe standing at the bus stop," she said and "the bus is a large target."
Some other parents who dropped their kids off in person were concerned to see police squad cars and sniffer dogs.
School officials have told students that they will have to spend their break times indoors for the time being.
The shootings have brought back memories of the October 2002 Washington-area sniper shootings that killed 10 people and terrorised residents of the US capital area and its suburbs.
One of the two suspected snipers in that case, John Allen Muhammad, 42, was sentenced to death last week for his role in one of the shootings.
The second alleged sniper, Lee Boyd Malvo, 18, is on trial separately.