How does Sancho know which locker is William's? The Gym Lady told him. Bolsa lead him to it. Sancho looked it up in the gym records. There is a sign with his name on it.

Sancho knows which locker is William's because the Gym Lady told him, Bolsa lead him to it, Sancho looked it up in the gym records, and there is a sign with William's name on it.