Update 10:33 p.m. EDT Monday: After Chamberlain had posted an apparent suicide note on his Facebook page earlier in the day, a witness told the Chronicle he saw police and federal agents make the arrest around 6 p.m. at a cafe near Crissy Field.

“He looked pretty surprised and frantic. He was asking for help,” said Morgan Manos, an Uber driver who witnessed the arrest and recognized Chamberlain from media photos. “He saw me recording (with a video camera) and asked me for help.”

Update 10 p.m. EDT Monday: The FBI arrested Ryan Chamberlain Monday evening, the San Francisco Chronicle reports. He was apprehended at Crissy Field near the Golden Gate Bridge.

Original story:

Federal investigators are looking for Ryan Kelly Chamberlain, 42, following the discovery of explosives in his San Francisco apartment.

FBI agent Peter Lee told reporters Sunday earlier reports Chamberlain also had ricin were untrue, KTVU, San Francisco, said.

More than two dozen FBI agents, police, fire department and hazardous materials crews raided Chamberlain's apartment Saturday.

Lee said he was unaware of any threats made by Chamberlain but he should be considered armed and dangerous. Lee, however, declined to say what materials were found in the apartment, the San Francisco Chronicle reported.

"He did possess explosives at his residence," Lee said.

Randy Bramblett, 32, a friend of Chamberlain's, told the Chronicle Chamberlain lost his job at the sports marketing firm Project Sport in November. Bramblett said since then, Chamberlain's behavior had gotten strange.

The University of San Francisco confirmed Chamberlain has been an instructor at the school. He also worked as an independent contractor during the 2012 NFL season, tweeting and posting Facebook links to the newspaper's coverage.