Former ATF agent says he regrets his last assignment. It changed how agencies approach undercover work.

Billy Queen with his Mongols jacket. Business Insider Billy Queen's undercover ATF mission infiltrating the Mongols was supposed to last a few months. It stretched on for two years, costing him his personal life and role as a father, he says. The operation's aftermath forced agencies to rethink undercover strategies and prioritize agent safety. After nearly two decades working undercover for the Bureau of Alcohol, Tobacco, and Firearms, Billy Queen was given the most dangerous assignment of...