Three Americans repatriated to the United States from Congo have been charged by the U.S. Justice Department with staging an elaborate coup attempt aimed at overthrowing the African nation’s government.

A fourth man alleged by prosecutors to be a bomb-making expert was also charged for aiding the plot.

The complaint stems from allegations that led to three of the defendants being detained in Congo and receiving death sentences. The sentences were later commuted to punishments of life imprisonment.

Following a long-running FBI investigation, the Justice Department accused the men of providing training, weapons and other support to a rebel army that was formed to try to overthrow the government last year.