José Lucas Costa da Silva peered over towards the warm-up area for the Brazilian ju-jitsu competition he was about to referee, faintly amused. It was early May 2023, and the 26-year-old martial arts instructor watched as one competitor in the high-school sports auditorium stretched and ran drills. He was wearing a white “gi”, a robe-like uniform, with some unusual accessories: sunglasses, a dark blue baseball cap and a medical mask. The man, whose name was listed as Mark Elliott, was a white belt, the beginner rank.

The tournament was taking place in Woodside, an affluent town close to Silicon Valley known for its sprawling estates enveloped by redwood trees. Da Silva, who is a ju-jitsu black belt, sometimes trained the neighbourhood’s nerdy, deep-pocketed residents for a fee. When the time came, da Silva beckoned Elliott and his opponent over. Only then did Elliott take off his mask and shades. A buzz swelled in the hall as people in the audience pulled out their phones to film. Da Silva noticed there were security guards in the periphery. “That’s when everyone realised he was there,” he said.

Financial Times