U.S. prosecutors are investigating whether Morgan Stanley misled investors about mortgage-derivatives deals it helped design and sometimes bet against, people familiar with the matter said, in a step that intensifies Washington’s scrutiny of Wall Street in the wake of the financial crisis.

Morgan Stanley arranged and marketed to investors pools of bond-related investments called collateralized-debt obligations, or CDOs, and its trading desk at times placed bets that their value would fall, traders said. Investigators are examining, among other things, whether Morgan Stanley made proper representations about its roles.

Among the deals that have been scrutinized are two named after U.S. Presidents James Buchanan and Andrew Jackson, a person familiar with the matter said. Morgan Stanley helped design the deals and bet against them but didn’t market them to clients. Traders called them the “Dead Presidents” deals.

The probe is at a preliminary stage. Bringing criminal cases involving complex Wall Street deals is a huge challenge for prosecutors. The government must prove beyond a reasonable doubt that a firm or its employees knowingly misled investors, a high bar. The government launches many criminal investigations that end without any charges being filed.

Morgan Stanley wasn’t among the biggest players in the CDO market. Although the firm made money on the Dead President deals, any profit was overshadowed by the $9 billion the firm lost on bullish mortgage bets in 2007, a person familiar with the matter said.

(Read More: WSJ)