There was a time, not long ago, when the economy was riding high and good times seemed nearly to be a guarantee. Now some of the very financial institutions that appeared to fuel that prosperity are teetering or have crashed and burned. And, as has been widely reported, those institutions and the individuals who drove the economic roller coaster may now face criminal investigation in connection with possible securities fraud. As the director of the FBI confirmed in a statement to Congress last fall, 24 large financial companies were then under investigation.