A 21-year-old man who is accused of killing a University of Idaho student and is under investigation in the separate slaying of a Boise State University student four days later is now believed by authorities to have shot a third victim, the Ada County sheriff's office said Friday.

John Joseph Delling, a former Boise resident who last lived in Antelope, Calif., has been linked to the shooting of Jacob J. Thompson, 23, on March 20 in Tucson, Ariz., Sheriff Garey Raney said. Thompson, who is originally from Boise, is now in rehabilitation after being shot in the face and chest, Raney told a news conference.

Delling was arrested Tuesday by police in Sparks, Nev., on a stolen car warrant issued by Ada County and a first-degree murder warrant issued by Moscow police in the death of UI senior David Boss, a former high school classmate of Delling at Timberline High School in Boise. Thompson also attended Timberline, Raney said.

Boss, a 21-year-old history major, was killed early Saturday in his off-campus apartment, shot twice in the head, police said.

Police have also identified Delling as a suspect in the death of Bradley Morse, 25, whose body was found Tuesday in a Boise city park pond near an office of the Idaho Department of Parks and Recreation where Morse worked as a janitor.

Family and acquaintances of Delling have said the young man was troubled and acting increasingly erratic before the slayings.

Delling apparently drove some 6,500 miles across much of the West, including California, Idaho, Oregon, Washington, Utah, Arizona and Nevada, during a four-week period prior to the killings in Idaho, Raney said.

"There is certainly a long pattern of behaviors that put people in fear," he said.

Thompson has identified Delling as his assailant, Raney said, The victim didn't know why he was targeted, he said.

Raney said a man believed to be Delling lured Thompson from his home in Tucson by tapping on the window and telling him he needed to move his truck, which was parked in front.

Once Thompson was inside his truck, Raney said, the man rode past on his bicycle and fired five times at the driver's side door.

Idaho authorities expect to prosecute Delling for the slayings before he would go to Arizona to face possible charges there.

"He'll come to Idaho and be charged with the murders," Raney said, adding investigators now believe Delling "laid in wait" outside the Boise Parks and Recreation building while Morse was finishing up his cleaning shift.