Nichols surrendered to authorities Saturday. Police said he had entered the apartment of a woman he didn't know and she managed to call 911 to report that he was there.
He was found in that apartment in the northern Atlanta suburb of Duluth, and gave up "without a struggle," said Maj. Edward Platt, with the Fulton County Sheriff's Department.
Police initially thought the woman in the apartment with Nichols might be a hostage, Atlanta Police Chief Richard Pennington said.
Authorities said later, however, that Nichols grabbed her as she was entering her apartment, but did not hold her hostage.
She was allowed to come out of the unit and speak with law enforcement officers shortly before Nichols surrendered.
Nichols was "not doing any talking," Pennington said.
The woman was being interviewed in an effort to determine the sequence of events in her encounter with Nichols, authorities said.
A blue pickup truck belonging to an Immigration and Customs Enforcement agent found slain Saturday was discovered at the scene, said Bureau of Alcohol, Tobacco, Firearms and Explosives spokesman Joe Green.
The pickup truck was spotted by Gwinnett County authorities apparently conducting a routine patrol, Platt said.
Police were watching the truck when the woman came out of her apartment and told them about Nichols. A SWAT team was summoned, along with FBI and Georgia Bureau of Investigation agents, and Nichols eventually surrendered.
But, he said, he was "somewhat surprised" Nichols surrendered without incident.
Police believe Nichols fatally shot Fulton County Superior Court Judge Rowland Barnes, court reporter Julie Ann Brandau and sheriff's deputy Sgt. Hoyt Teasley after he overpowered deputy Cynthia Ann Hall and stole her gun while Hall was taking him from a detention area into Barnes' courtroom.
He was transported to FBI headquarters in Decatur, Georgia, in DeKalb County. If federal firearms charges are filed, he will appear before a magistrate sometime this afternoon in Atlanta, Green said.
The manhunt for Nichols, 33, was described as being the biggest in Georgia history.
Video footage showed Nichols being handcuffed and put into a dark-colored SUV by authorities.