Charles A. McCoy Jr., 28, lived with his mother within miles of where the gunman's bullets killed a passenger, shattered windshields, dented school buses and drilled into homes and a school.
"McCoy has had mental health issues in the past and is currently not on medication," the Franklin County Sheriff's Office said in a bulletin released to police departments across the country. "He is believed to have suicidal or homicidal tendencies."
McCoy's sister Amy Walton pleaded Tuesday for him to give himself up.
"Charlie, we all love you very, very much and we're all concerned for your well-being," she said, reading a statement in front of the home where McCoy lives with his mother. "Mom and I need you to call us. We will arrange for you to come home. We love you, we miss you."
Authorities identified McCoy as a suspect Monday and released his picture, vehicle description and license plate.
Walton did not take questions after reading the statement and walked back into the house. McCoy's parents, both state employees, could not be reached Tuesday and neither one was at work.
"What we want to do most of all is to find him," says Chief Deputy Steve Martin, of the Franklin County Sheriff's office. "We believe he's bought another gun."
Martin would not say what evidence led investigators to McCoy, but newspaper and television reports said Tuesday that McCoy's family gave authorities at least one of his guns.
The Columbus Dispatch, citing unidentified sources, said a relative contacted police and said McCoy could be a suspect. It said McCoy's father, Charles Sr., later gave police a 9 mm Beretta handgun, and on Monday it was matched to some of the bullet fragments recovered in the shootings.
The bulletin said McCoy is believed to have a semiautomatic pistol and ammunition.
Since May, two dozen sniper shootings have targeted vehicles and buildings around Interstate 270, which circles Columbus, and other highways. Most of the shootings have happened since October; the latest was on Feb. 14.
Investigators filed an arrest warrant late Monday for McCoy on a charge of felonious assault in a Dec. 15 shooting that damaged a house.
McCoy's mother, Ardith, filed a missing persons report with Columbus police on Monday, saying she had not seen her son since Friday.
She said he was upset over a possible move and withdrew $600 from a bank account, saying he was going to a restaurant-bar known for its array of video games.
As word of the manhunt spread through the town where McCoy was a running back on the high school football team 11 years ago, his former coach was among those stunned by the news.
"You hope and pray he does the right thing now. You hope he turns himself in," said Brian Cross, who coached McCoy for four years at Grove City High School.
Cross, who now coaches at Canton McKinley High School, remembers McCoy as a "tough, hard-nosed kid" who could be difficult at times but tended to be on the quiet side.
"He was an ornery kid, but a lot of kids are ornery at that age. I don't remember him doing anything extreme," Cross said.
Neighbors on McCoy's street of tidy, vinyl-sided homes said they didn't know much about the suspect or his mother.
"They pretty much stayed in their house when they were home except when he was working in the yard," said Nicole Sewald, 28, who lives across the street. Her 8-year-old son attends Hamilton Central Elementary School, where one of the sniper's bullets struck a window in November.
The McCoys moved there about a year ago, did some repairs and put the house back up for sale, she said.
The garage doors at the house had been splattered with eggs Tuesday. Three eggs were stuck to the garage's two tan doors. Police said they did not know who hurled the eggs or when they were thrown.
A hand-written sign on the door at his father's house a few miles away said, "We do not want to speak to the media."
In the three most recent shootings, witnesses described seeing someone aiming at them while standing next to a car. Their descriptions of the suspect and car were similar to information the sheriff's office released Monday.
The suspect is 5-foot-8, 185 pounds with brown hair and green eyes, the sheriff's office said Monday. The car is a dark green 1999 Geo Metro with a black hood.
From the beginning, Martin had said investigators believe the shooter is familiar with the area around I-270. Although the last four shootings were on other highways, most of those that occurred through January were within about a 10-mile stretch of the interstate.