The Justice Department has accused a network of North Korean and Chinese citizens of secretly advancing North Korea’s nuclear weapons program by channeling at least $2.5 billion in illicit payments through hundreds of front companies. The indictment, unsealed Thursday in Washington's federal court, is believed to be the largest criminal enforcement action ever brought against North Korea. The 33 defendants include executives of North Korea's state-owned Foreign Trade Bank, which in 2013 was added to a Treasury Department list of sanctioned institutions for transactions that facilitated the nuclear proliferation network, and cut off from the U.S. financial system.