(CNN) Robert Mueller's team declined to prosecute Donald Trump Jr. and other members of the campaign for campaign finance violations for their participation in the June 2016 meeting at Trump Tower, in part, because they couldn't prove that they "willfully" violated the law.

"Taking into account the high burden to establish a culpable mental state in a campaign-finance prosecution and the difficulty in establishing the required valuation, the Office decided not to pursue criminal campaign-finance charges against Trump Jr. or other campaign officials for the events culminating in the June 9 meeting," Mueller's team explained.

"The Office ultimately concluded that, even if the principal legal questions were resolved favorably to the government, a prosecution would encounter difficulties proving that Campaign officials or individuals connected to the Campaign willfully violated the law," the team continues.

On June 9, 2016, Trump Jr., Jared Kushner, and then-campaign chairman Paul Manafort met with Russian lawyer Natalia Veselnitskaya at Trump Tower.

According to tweets published by Trump Jr. in July 2017 , publicist Rob Goldstone sent Trump Jr. an email on behalf of his client Emin Agalarov to suggest the meeting regarding potential dirt on Clinton.

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