Some Wall Street investors made money as the mortgage market boomed; others profited when it fell apart.

Having reaped big gains during both of those turns, Greg Lippmann, a former star trader at Deutsche Bank, is now catching the next upswing: buying the same securities built from mortgages that he bet against before the financial crisis erupted.

Mr. Lippmann is joined by other big-money investors — mutual funds like Fidelity as well as hedge funds — in riding a wave of interest in the same complex loan pools that nearly washed away the financial system.

The attraction is the price. Some mortgage bonds are so cheap that even in the worst forecasts, with home prices falling as much as 10 percent and foreclosures rising, investors say they can still make money