Police in San Francisco have arrested 42-year-old Ryan Kelly Chamberlain, concluding a nationwide manhunt following the discovery of explosive materials in his apartment. (Reuters)

A San Francisco social media expert and political consultant suspected of possessing explosives has been captured after a three-day manhunt, news reports say.

The San Francisco police nabbed Ryan Kelly Chamberlain II, 42, on Monday evening in his white 2008 Nissan Altima near Crissy Field, south of the Golden Gate Bridge.

During the weekend, authorities had announced they were searching for Chamberlain after FBI agents said they found explosives in his San Francisco apartment.

“Anyone who has the means, methods and access to make a bomb should be considered armed and dangerous,” FBI spokesman Peter Lee said before the arrest.

CBS SF Bay Area reported:

Authorities said Chamberlain disappeared before FBI agents found explosives during a raid of his apartment at Polk Street and Van Ness Avenue over the weekend.

Before he disappeared, Chamberlain posted a manifesto about his battles with depression. The note chronicled relationship, financial and emotional troubles he had dealt with in recent years, referring to them as the “dark times.”

On Monday morning, Chamberlain made posts on social media denying claims from authorities that he is armed and dangerous.

An anonymous official told the Associated Press Chamberlain was arrested without incident and is in the custody of the FBI, where he is being processed or undergoing interrogation. A law enforcement official who asked not to be identified told the San Francisco Chronicle he was booked on suspicion of possessing explosives in violation of federal law.

Lee gave no further details on the investigation. The AP reported the affidavit and search warrant used to go through Chamberlain’s home are sealed.

Chamberlain is known in Bay Area media and political circles. He helped Lt. Gov. Gavin Newsom (D) in his winning 2003 San Francisco mayoral campaign, the Chronicle reported.

A news conference on the arrest was planned for Tuesday at 8:30 a.m. at the San Francisco Federal Building.