Officials from the Departments of Justice and Treasury appeared on Capitol Hill Wednesday to underscore transnational crime organizations' penetration of the U.S. financial system and to push for new legislation expanding the country's anti-money laundering laws.

Jennifer Shasky, the head of the Justice Department's Money Laundering unit, said that international crime syndicates had become increasingly adept at using loopholes in the U.S. legal system to hide and launder their ill-gotten gains, necessitating the need for wide-ranging...