Testimony in the Sean “Diddy” Combs sex trafficking trial has opened a window into what prosecutors say was the sordid world of group sex, drugs and violence beneath his glittering, jet-set persona.

Casandra Ventura, the singer known professionally as Cassie, ended four days of sometimes grueling testimony about being abused by Mr. Combs.

Representatives for Justin Bieber said on Thursday that he is not a victim of the crimes alleged in Sean “Diddy” Combs sex trafficking trial, breaking his silence to address online speculation that has swirled for months over the teenage heartthrob and the disgraced music mogul.