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.
"Rick Gates had his hand in the cookie jar, and he couldn't take the risk that his boss might find out", Zehnle said.
Buell also said it's very hard to find a strategy for defending against fraud charges in cases with an extensive paper trail.
Prosecutors on Monday went through a list of overseas corporations and Gates testified that all of them were controlled by Manafort and contained income earned by his political consulting work.
Some of the manoeuvrers were at the request of Mr Gates, while others implicated Mr Manafort, Ms Laporta testified.
Manafort has pleaded not guilty to 18 counts of bank and tax fraud and failing to disclose foreign bank accounts. Gates also worked for the Trump election campaign.
"They probably have hundreds and hundreds of emails", the former USA prosecutor said. The White House says Mr. Trump feels his former campaign chair is being treated unfairly.
Under cross examination, she said at the time she believed Manafort was directing Gates' actions and "knew what was going on". Special counsel Robert Mueller originally charged Gates alongside Manafort, but Gates reached a plea deal with Mueller in exchange for cooperating in the investigation.
Prosecutors surprised Judge T.S. Ellis last Wednesday when Uzo Asonye, a special counsel attorney, suggested that Gates "may not" take the stand.
The most critical moment in the financial fraud trial of former Trump campaign chairman Paul Manafort will likely arrive this week with the testimony of his "right-hand man" - the person defense attorneys blame for any crimes.
There was no mention of President Trump or his campaign, but this trial is the first big public test for the special counsel.