accomplice

noun2

1. •
   a person who takes part with someone else in a crime

   • Childless Arturius, vastly rich before, / Thus by his Losses multiplies his Store: / Suspected for Accomplice to the Fire, / That burnt his Palace but to build it higher. — 1693
2. •
   (rare) A cooperator.

   • Successe vnto our valiant Generall, / And happinesse to his accomplices. — 1591