Several months ago, the FBI became interested in the Facebook account of Everitt Aaron Jameson, a 26-year-old Modesto tow truck driver and former Marine.

Acting on tips from an informant, authorities said they saw that Jameson liked and loved pro-Islamic State and pro-terrorism Facebook posts. In the coming weeks, the FBI alleged, Jameson would plot a Christmas suicide terror attack on San Francisco’s Pier 39, a popular tourist destination.