NEW YORK, May 18 — The first week of testimony in the sex trafficking trial of Sean “Diddy” Combs included a witness core to the case: Casandra Ventura, the music mogul’s ex-girlfriend who accuses him of harrowing abuse, coercion and rape.

Combs, 55, is facing federal charges of sex trafficking and leading an illegal sex ring that enforced its power with crimes including arson, kidnapping and bribery—and faces life in prison if convicted.