As an assistant U.S. attorney, he investigated and prosecuted a wide range of federal crimes including racketeering, murder, money laundering, securities fraud, firearms and narcotics offenses, tax evasion, and terrorism.

During his tenure, Kim helped secure convictions of a number of high-ranking organized crime figures including Peter Gotti, boss of the Gambino Family, for conspiring to kill Salvatore "Sammy the Bull" Gravano.

[4] Kim's term was notable for the continued prosecution of high-profile terrorism cases,[5][6] pursuing a prison term for Anthony Weiner following his guilty plea to a federal obscenity charge,[7] and for securing the conviction of Mehmet Hakan Atilla, a Turkish banker, on fraud and conspiracy charges in a billion-dollar scheme to help Iran evade American financial sanctions via Turkish banks, despite an investigation of the American prosecutors by the government of Turkey.

[8] On November 30, 2017, Kim announced the sentencing of Aharon Goldberg, Shimen Liebowitz and Binyamin Gottlieb, three organizers of the Kiryas Joel murder conspiracy who had tried to force an end to their intended victim's marriage under Jewish marital law.

[11][12] In coordination with the New York Office of Attorney General, Kim served as an independent investigator into the accusations of sexual assault and harassment against Governor Andrew Cuomo.