Jean-Luc Brunel, a longtime French modeling agent who was detained in December 2020 as part of an inquiry into allegations of rape, sexual assault and sexual harassment, was found dead in his cell on Saturday, the Paris prosecutor's office said.

The investigation, opened in August 2019, was a preliminary inquiry into whether late financier and convicted sex offender Jeffrey Epstein had committed sex crimes on French territory or against French victims.

Brunel, 76, who had...