Menlo Park Police Cmdr. Dave Bertini said officers followed standard procedure and cleared the buildings, located at 1 Hacker Way, until determining that the campus was safe.
"I'm not even sure it was directed against Menlo Park Facebook," he said.
Meanwhile, Facebook's employees huddled in the central courtyard until about 8:30 p.m., when shuttle buses were cleared to take everyone home, sources said.
Sgt. Newman said the investigation into the threat remains "open and active." No new information was available by the Almanac's press deadline on March 17.
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