Acosta knew 50+ Epstein victims but cut a deal: state case and 16 months in jail

I tried a federal sex trafficking case with 1 victim. Trafficker got 20 yrs in jail.

Acosta knew of 50+ Epstein victims. Federal charges carry 15 yrs - life, but Acosta cut a deal: state case and 16 months in jail.

How many victims did Acosta need to bring a federal case?