BOISE, Idaho – The investigation began with a university student slain in the Idaho town of Moscow. By week's end, authorities were unraveling the killing of a second young man, whose body was dumped in a Boise pond, and the wounding of a college student in Tucson, Ariz.
Police say the common thread is 21-year-old John Joseph Delling, a former high school classmate of two of the shooting victims. The third attended a nearby high school at about the same time.
Delling is now jailed in Nevada, but authorities fear there could be more victims along the path of his monthlong, 6,500-mile road trip across the West.
"We're concerned that this is not over yet," Ada County Sheriff Gary Raney said. "We've been overwhelmed with these possibilities."
The violence may have started March 20, when University of Arizona student Jacob J. Thompson was lured out of his Tucson home and then shot three times, in the face, shoulder and arm, Raney said. Thompson survived, and recently picked Delling out of a photo lineup.
Eleven days later, University of Idaho student David Boss apparently let someone into his Moscow apartment, only to be shot twice in the head at close range. On Monday night, Bradley Morse, 25, was shots in the head as he left his job as a janitor at the Idaho Department of Parks and Recreation in Boise. His body was found in a nearby pond.
Phone records show Delling called Boss about the time he was slain, and Delling was arrested April 3 in Sparks, Nev., driving Morse's car.
"All these seem to be specifically targeted, at least in time and place," Raney said. "The connection probably goes back four or six or eight years ago — that's our best guess."
After discovering Boss's body, Moscow police warned three other former classmates of Delling's that they may be in danger, Assistant Police Chief David Duke said. Authorities would not release their names, but said all been involved in an incident with Delling during his sophomore year at Timberline High School. Additional details weren't released.
Delling, who last lived in Antelope, Calif., was arrested on a stolen car warrant issued by Ada County and a first-degree murder warrant from Moscow police in connection with Boss's death. He was still awaiting extradition to Idaho, and Reno Justice Court officials said he had not been appointed a lawyer.
Delling has declined to talk to reporters, said Washoe County, Nev., sheriff's Deputy Brooke Keast.
Family and acquaintances of Delling have said the young man was troubled and acting increasingly erratic.
Starting March 1, Delling drove some 6,500 miles through California, Idaho, Oregon, Washington, Utah, Arizona and Nevada, Raney said. Police used financial records and rental car records to track his movements.
In the Tucson attack, Thompson was lured from his home after someone tapped on his window and yelled that he needed to move his truck, which was parked out front at an awkward angle, Raney said.
As Thompson moved the truck, he asked a man sitting on a bicycle if he was the one who wanted the truck moved, Raney said. The man on the bicycle approached the truck and fired five times at the driver's side door, Raney said.
Thompson was hit three times, with one bullet hitting his face and lodging in the back of his head.
Despite his injuries, Thompson can now speak and identified Delling from a photo lineup, Raney said.
"Often crimes are a matter of who did it. This is a matter of why did he do it," Raney said. "Thompson has lived at the University of Arizona for the past three years. Was it something that happened four years ago? Eight years ago? Ten years ago?"Click here for FOXNews.com's Crime center.