Ryan Kelly Chamberlain II was taken into custody by the FBI Monday evening, two days after the agency allegedly discovered explosive materials in his San Francisco apartment during a raid.

Police say that Chamberlain, a social media manager, was arrested near the Golden Gate Bridge after a day of authorities chasing him throughout the city.

"We had been close to him all afternoon," a source tells ABC News. "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."

On Monday, an alleged suicide note Chamberlain scheduled to post went live. "You're reading this. That means we probably don't know each other anymore, and I owe everyone an explanation," his note starts. "I've timed this note on a Hootsuite delay, and now it's live, which means I wasn't around to stop it from posting."

He also tweeted Monday hours before his arrest by police:

Court documents are currently under seal, but ABC News has details of the alleged explosive materials found in Chamberlain's home:

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.

Morgan Manos, an Uber driver, was in San Francisco's Crissy Field when Chamberlain was arrested and got video of his arrest:

[Image via ABC News]