The report indicates that information was leaked to both the New York Times and Wall Street Journal while Mickelson came under fire for a stock purchase he made based on a tip from noted sports bettor Billy Walters.
A recent filing by the Department of Justice described the agent in question as "a significant source of confidential information leaked to reporters ... about the underlying investigation." The leak will reportedly be investigated by government officials as a possible "violation of criminal procedure."
The report notes that the leak resulted in several articles being published about Mickelson in May and June 2014. It was also during that time that FBI officials approached Mickelson at the Memorial Tournament following the completion of his first round.
Mickelson was never charged with a crime, though in May 2016 Mickelson was named as a relief defendant by the Securities and Exchange Commission and subsequently agreed to pay back more than $1 million from a purchase of Dean Foods stock that was based on "material, nonpublic information" acquired from Walters.