Alexandria, Virginia (CNN) Rick Gates, the key prosecution witness in the tax and fraud trial of former Trump campaign chairman Paul Manafort, testified Monday he had committed crimes alongside and at the direction of his former partner -- and had also stolen from Manafort himself.

In stunning testimony, Gates stated he and Manafort had 15 foreign accounts they did not report to the federal government, and knew it was illegal. Gates said he did not submit the required forms "at Mr. Manafort's direction."

Gates then admitted that he also turned the tables on Manafort -- cheating him out of "several hundred thousand" dollars by submitting false expense reports that were paid out of some of the undisclosed foreign bank accounts in Cyprus.

The testimony from Gates, a former adviser to Donald Trump, comes after reaching a plea deal with special counsel Robert Mueller earlier this year to testify against his former partner in a lucrative international political consulting firm.

Manafort stared directly at Gates as he read aloud the details of his plea agreement, which could see him receive a reduced sentence, at the direction of a prosecution lawyer.

Read More