The Justice Department has questioned several former executives at Lehman Brothers as part of its criminal investigation into whether they sold supposedly safe, liquid securities to clients while knowing that the market for the securities was drying up.

Prosecutors from the US attorney's office in Brooklyn and lawyers from the Securities and Exchange Commission in recent weeks interviewed several former executives who ran Lehman's auctioneer-securities business, these people said. Auction-rate securities are short-term debt instruments in which the interest rates reset at periodic auctions.