In his years as a US federal agent, Tigran Gambaryan helped to lead landmark investigations that took down cryptocurrency thieves and money launderers, dark-web drug dealers, and even crypto-funded child exploitation networks. Now, in his post-government role at the cryptocurrency exchange Binance, he has become the target himself of a very different sort of federal crypto crackdown: For the past two weeks, he and another Binance executive have been detained against their will by Nigerian offici...