Ryan Kelly Chamberlain II, the subject of a nationwide manhunt after explosive materials were allegedly found in his San Francisco apartment, was taken into custody by the San Francisco Police Department and the FBI, an FBI spokesman said.
A law enforcement source briefed on the case told ABC News that Chamberlain was taken into custody Monday "right under the Golden Gate Bridge" after police came across a white 2008 Nissan Altima, matching the description of Chamberlain's car.
Authorities say Chamberlain also used his ATM card as police were searching for him -- an indication he wasn't working that hard to stay under the radar.
The capture came after a day of dramatic and cinematic cat-and-mouse with the hunted man.
"We had been close to him all afternoon," the scource said. "We never could quite get to where he was. We would find out he was in a particular location 10 or 15 minutes after he was there. He was working his way through the city."
Chamberlain was being trailed by a sizeable task force, made up of FBI agents and local cops.
He was wanted for allegedly possessing explosive materials, and when FBI spokesman Peter Lee announced the bureau's call for public assistance in the manhunt, he said Chamberlain should be considered armed and dangerous.
Despite that, Lee also said Sunday that Chamberlain "has not made any threats that I know of."
"There is no threat to public safety at this time that we know of," he said.
The FBI spokesman made similar remarks as he briefed reporters on developments in the manhunt.
Chamberlain was expected to make his first appearance in federal court at 9:30 a.m. Tuesday.
Both the affidavit and the search warrant in the case were under seal.
Chamberlain had been wanted since Saturday, when FBI agents, San Francisco police and fire crews, and a hazardous materials team swarmed his apartment in the Russian Hill neighborhood.
There were initial reports that law enforcement sources told reporters a large amount of ricin was found, but Lee said Sunday those reports were false.
Instead, he said, explosive materials were found. A law enforcement source said an explosive device designed to maim or killed could have been made from the materials in Chamberlain's apartment, though a fully functioning bomb was not found there.
A letter posted on Chamberlain's Facebook page Monday that said it was "timed ... on a Hootsuite delay," described increasing financial and personal difficulties the author said he faced.
"In the span of a few months, everything that mattered to me betrayed me," the letter says.