Ryan Chamberlain, the San Francisco media consultant who became the focus of a manhunt after agents allegedly found explosives in his apartment, was arrested near Crissy Field on Monday evening, the FBI said.

Chamberlain was taken to a police station and booked on suspicion of possessing explosives in violation of federal law, said a law enforcement source who asked not to be identified.

A police bomb squad, meanwhile, used a robot mechanism to search his car.

According to the law enforcement source, police on patrol had spotted Chamberlain’s white four-door sedan parked outside the Beach Hut Cafe, in view of the Golden Gate Bridge, at 6:22 p.m.

Hours earlier, Chamberlain posted an apparent suicide note on his Facebook page and the FBI responded to a possible sighting at a Lower Haight bar.

At the scene of the arrest, a witness reported seeing police and federal agents detain Chamberlain outside the cafe. “He looked pretty surprised and frantic. He was asking for help,” said Morgan Manos, an Uber driver who recognized Chamberlain. “He saw me recording (with a video camera) and asked me for help.”

Manos said Chamberlain was wearing shorts, a sweatshirt and a beanie and looked scared. “They took him down hard,” Manos said.

The law enforcement source said Chamberlain got out of the car and was arrested without incident, although Manos’ video showed Chamberlain struggling as officers took him to the ground.

Here is Manos’ video of the arrest, via KGO-TV:

And here’s another view of the arrest, courtesy of Phillip Hirsch:

Tweets from Chronicle staff members and others on the arrest: