Three former investment advisers have been sentenced for their roles in a $1 billion high-yield investment fraud scheme, the FBI said Wednesday. William J. Ferry, a former stock broker and investment adviser, was sentenced Tuesday to 15 months in prison, while Dennis J. Clinton, a former real estate investment manager, and Paul R. Martin, a former senior vice president and managing director of Bankers Trust, were sentenced to 30 months each, the FBI said in a news release. All three were convicted July 31, 2012, of conspiracy, mail fraud and wire fraud in a case in which they tried to defraud an investor who turned out to be part of an undercover FBI team posing as investors and investment managers. Between February and December 2006, Ferry, Clinton, Martin and others promised potential investors "an extremely high return at little or no risk to principal," the FBI said. Ferry, 71, of Newport Beach, Calif., acted as an underwriter and represented himself to be a federal compliance officer. Clinton, 65, of San Diego, acted as a troubleshooter on compliance issues and the transfer of funds to a Swiss bank, and Martin, 64, of New Jersey, pretended to be a banking expert, the FBI release said. Brad Keith Lee of California and John Brent Leiske of Oregon previously pleaded guilty in the case. Lee was sentenced in 2010 to 24 months in prison and Leiske was sentenced in February to 120 months.