Authorities had been searching for Derek W. Potts since Monday afternoon, when they allege he marched into the state Capitol and shot 51-year-old William Wozniak in the chest, then stowed his gun in his car trunk and drove away.
"He's in custody," Deputy Police Chief Jim Burton said. "We're interviewing him now."
Phillip Giger, 50, who lives in the neighborhood where Potts was apprehended, said he was making coffee when he heard several car doors slam shut. He looked out the window and saw more than a dozen police cars and a man who was handcuffed and put in a squad car.
"There were no sirens, not a one," he said. "They were so quiet my dog didn't even notice it."
The Sangamon County state's attorney's office obtained an arrest warrant Monday night accusing Potts of murder, burglary and more.
Police said they know of no motive for the shooting or connection between Potts and his alleged victim. Wozniak died shortly after the attack in a hospital operating room.
"We have no idea why he came here and did this," said Col. Larry Schmidt, chief deputy director of the Secretary of State's police force.
The Legislature was not in session. The Capitol was locked down for about an hour after the shooting, security was tightened at nearby schools.
The Capitol building doesn't have metal detectors, and the security guards are unarmed. Several people saw the gunman leaving, and officials also were reviewing footage from surveillance cameras in the area, Schmidt said.