SAN FRANCISCO — Federal investigators said a search of a social media expert’s apartment in San Francisco turned up ball bearings, screws and components needed to make a homemade bomb designed to kill or maim, according to an affidavit unsealed Tuesday.

Investigators said they found the materials inside a bag at the apartment of Ryan Kelly Chamberlain during a search over the weekend. The discovery prompted a manhunt for the 42-year-old Chamberlain that ended with his arrest Monday in San Francisco.

The bag also contained a circuit board, screw top glass jar with batteries, a wire and a powdery green substance believed to be explosive material, FBI Special Agent Michael Eldridge said in the document.

“FBI bomb technicians believe that the circuit board described above was designed to serve as a remote control, allowing detonation of the device from afar,” Eldridge said. “They further believe that the device was designed to maim or kill a human being or human beings.”

The FBI has not said what, if any, plans Chamberlain might have had for the device, or how they were alerted to the material.