Speaking Saturday at the annual meeting of Berkshire Hathaway, Buffett said he should have pressed David Sokol for more information about the investment and Sokol's personal holdings in the company's stock.
Buffett said Sokol, who had recently purchased $10 million in Lubrizol stock, violated Berkshire policy by buying the stock and them pushing Berkshire to do the same. The Wall Street Journal said Sokol's stake gained about $3 million as a result.
"I obviously made a big mistake not saying, 'Well, when did you buy it?'" Buffett said.
Sokol's attorney responded with a statement accusing Buffett of using Sokol as a scapegoat and denying any wrongdoing.
"David Sokol is deeply saddened that Mr. Buffett, whom he considered a friend and mentor, would disparage him as he has done today," said lawyer Barry Levine.