The Federal Bureau of Investigation (FBI) is investigating whether insider trading took place in Heinz shares ahead of the food giant's historic deal with Warren Buffett's Berkshire Hathaway.
Berkshire Hathaway and investment firm 3G agreed to pay $23bn in cash for the ketchup maker last week.
However, shortly after the merger was announced options market traders noticed there had been unusual activity the previous day.
The US Securities and Exchange Commission (SEC) has filed a suit against traders who used a Goldman Sachs account in Switzerland to trade on possible insider knowledge of the deal.
However, in the latest twist, the FBI has said it will now join the investigation, stating it is aware of "trading anomalies."
"The FBI is aware of trading anomalies the day before Heinz's announcement. The FBI is consulting with the SEC to determine if a crime was committed," said an FBI spokesperson.
The SEC believes that some traders made $1.7m from insider knowledge so it obtained an emergency court order to freeze assets in a Swiss-based account.
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.
After the official announcement of the deal Heinz's share price rose by 20%.
Caring for children and elderly relatives
Similar to June 2007
Square Mile’s series of informal interviews
Fine reduced to £60,000
Two roles created