A long-running insider trading investigation by the FBI, the Securities and Exchange Commission and federal prosecutors in Manhattan is focusing on a well-known gambler, a widely-popular championship golfer and a 78-year-old billionaire.

The Wall Street Journal and the New York Times reported on Friday that federal authories are looking into whether investor Carl Icahn gave an early tip to gambler Billy Walters, who may then have passed it along to Masters champion Phil Mickelson. It's not clear whether Mickelson knows Icahn.

Icahn, and a lawyer for Mickelson, told the Wall Street Journal they had done nothing wrong; Walters declined to comment.

The authorities are looking at trades of two different stocks. According to the Times, feds are investigating whether Icahn may have shared information about one of the stocks, Clorox. At the time Mickelson and Walters placed their Clorox trades, in 2011, Icahn was mounting a takeover bid for the company. The bid failed. 

Recently, the SEC sent Icahn a request for documents about his Clorox dealings.

It would not be illegal for Icahn to reveal information about his takeover plan, unless doing so would breach a duty of confidentiality to his investors.

The second trade that authorities are investigating relates to Dean Foods (and does not involve Icahn). Walters and Mickelson placed their trades around August 2012; one of the company's subsidiaries had a public stock offering soon thereafter. The issue, according to the New York Times and the Wall Street Journal, is whether Walters had a source inside the company.

Walters, a high-profile high-roller, was acquitted of illegal gambling charges in 1992. Mickelson has won five major championships in his pro career. His popularity with golf fans--and his squeaky-clean private life--have brought him millions in endorsement deals. Icahn is a legendary activist investor.  

The investigation has already proceeded for two years, and authorities have not accused any of the men of wrongdoing.