On Friday, the Securities and Exchange Commission (SEC) obtained an emergency court order to freeze assets in a Swiss account, which was used to generate more than $1.7m from trades in advance of the sale being announced.
Yesterday, the FBI said it was joining the inquiry. "The FBI is aware of the trading anomalies," a spokesman said. "The FBI is consulting with the SEC to determine if a crime was committed."
Unnamed traders took “risky bets” that Heinz’s share price would rise before there was any “public awareness” that Buffett’s Berkshire Hathaway (NYSE: BRK-A - news) investment group and 3G Capital had agreed a deal for the food manufacturer, the SEC said in a statement.
The traders bought call options the day before the announcement, putting them in a “position to profit substantially” when the deal was announced, the SEC said.
Following the surprise revelation on Thursday shares in Heinz rose by almost 20pc and trading volume rose more than 1,700pc compared with the previous day.
The SEC said the timing and the size of the trades were “highly suspicious” because the Zurich-based account through which the call options were bought had “no history of history of trading Heinz securities in the last six months”.
The $28bn deal by 82-year-old Mr Buffett is the biggest ever takeover in the food industry.