Rick Gates, Paul Manafort’s former right hand man, has been called to testify in the trial the former chairman of Donald Trump’s presidential campaign.

Gates pleaded guilty in February to a bank fraud conspiracy charge in exchange for testifying against his former boss.

Experts have billed Gates as the star witness in the tax evasion and bank fraud trial that Special Counsel Robert S. Mueller III is prosecuting against Manafort who is facing 18 counts of tax evasion.

The defense has accused Gates of embezzling millions of dollars from Manafort, claiming he had sweeping authority over his boss’s business and personal expenses and that he abused that authority by going behind Manafort’s back to deceive his bookkeeper and the accountants who prepared Manafort’s taxes.

On the prosecution’s projected evidence list are 23 email exchanges between just Manafort and Gates.

Prosecutors will move to admit those exchanges to the record when Gates takes the stand.

The emails will provide the jurors a glimpse into the private conversations between Manafort and Gates, the man to whom he entrusted his personal and business finances.

“They probably have hundreds and hundreds of emails,” the former U.S. prosecutor said. “The fact that they only chose 23, those are probably the ones they think are most damaging.”

The contents of those emails — and how Gates interprets them before the court — could help either save or sink Manafort.

Prosecutors are trying to craft a narrative through the various vendors, bookkeepers, and accountants who have testified that Manafort, through Gates, directed his own illicit transactions.

“It’s kind of leading up to Gates’ testimony that, ‘Yep, this is what he was telling me to do,’” the former U.S. prosecutor said.

Jeff Cirillo and Eric Garcia contributed to this report.