As Paul Manafort’s trial for bank and tax fraud entered its second week in federal court in Alexandria, Virginia, the intensity ratcheted up significantly Monday afternoon when the prosecution called former Manafort business partner Rick Gates to testify. Gates, like Manafort, was charged with federal crimes for his overseas work with the former Trump campaign chairman, but after initially professing his innocence agreed to a plea deal with Robert Mueller’s team in February. As part of the deal, Gates agreed to plead guilty to two felony charges and to cooperate with the special counsel investigation. Gates’ plea deal—for which he could face six years in prison or none at all, depending on the value of his help to prosecutors—transformed the former Trump aide from potential target into star witness in the Manafort trial.

During his testimony Monday, Gates gave damning testimony against his former boss, as well incriminating as himself, admitting to stealing hundreds of thousands of dollars from Manafort in addition to knowingly committing crimes at Manafort’s direction.

From the New York Times:

Asked by prosecutors whether he was involved in any criminal activity with Mr. Manafort, Mr. Gates responded, “Yes.” Mr. Gates also testified that he and Mr. Manafort held 15 foreign bank accounts that were not disclosed to the federal government. Mr. Gates said the required financial filings were not submitted “at Mr. Manafort’s direction.” Mr. Gates admitted to a wide variety of crimes, including bank fraud, tax fraud, money laundering, lying to federal authorities, lying in a court deposition and stealing hundreds of thousands of dollars from Mr. Manafort’s accounts by falsely claiming expenses.

Gates is one of 35 potential witnesses for the prosecution, but his links not only to Manafort but the Trump campaign make him potentially dangerous for the administration. Gates was the deputy chairman of the Trump campaign under Manafort and stayed on even after Manafort’s ouster, serving as campaign liaison to the Republican National Committee. Gates then helped raise vast sums of money for the Trump inauguration as the deputy chair of the inaugural campaign. Manafort’s defense team is expected to counter Gates’ claims that Manafort was a co-conspirator in a vast financial conspiracy by showing that Manafort was largely duped by Gates, who stole from Manafort, kept crucial information from him, and was the instigator of the political consulting firm’s financial misdealing.