A bodybuilder posing as a Muslim convert was welcomed into a California mosque. When he showed signs of extremism, members reported him to the FBI, only to learn that he was their informant. Now, their story is before the Supreme Court. Today’s show was produced by Haleema Shah, edited by Matt Collette, engineered by Cristian Ayala and Paul Mounsey, fact-checked by Laura Bullard and Will Reid and hosted by Sean Rameswaram. Transcript at vox.com/todayexplained Support Today, Explained by making a financial contribution to Vox! bit.ly/givepodcasts Learn more about your ad choices. Visit podcastchoices.com/adchoices