As a symbol of late 1990s Silicon Valley investment-banker excess, perhaps no one surpasses Frank Quattrone of Credit Suisse Group's(NYSE: CSR) Credit Suisse First Boston. From his perch in California, he ran a technology investment-banking group that underwrote many infamous tech initial public offerings in 1999 and 2000.

The mustached Quattrone has been under fire the last two years for his aggressive practices and suspicions of misconduct. CSFB has stood by its man, though. Quattrone's role diminished, but he remained with the company despite heavy criticism.

However, the banker's luck may have just run out. CSFB placed him on administrative leave today in response to newly discovered emails that seem to indicate Quattrone may have instructed his underlings to get rid of important documents related to IPO investigations. The National Association of Securities Dealers (NASD) gave Quattrone notice on Friday, saying it may file civil fraud charges against him.

At issue for the NASD is Quattrone's involvement with research analysts and the question of "spinning," the practice of awarding shares in hot IPOs to investment-banking clients. Quattrone had so-called "Friends of Frank" accounts for Silicon Valley executives who were allocated IPO shares.

Now, according to CSFB, an email dated December 5, 2000 indicates that not only was Quattrone aware that CSFB was going to be investigated for its IPO practices, but that he encouraged the "clean up" of files around the issue.

Previously, Quattrone had claimed no knowledge at all of any pending investigations. Another email, dated December 3, 2000 from CSFB's former in-house lawyer David Brodsky to Quattrone, notified the banker that CSFB would be investigated and that the firm had already received a grand jury subpoena.

Oh dear. Lying and destroying evidence in the midst of a grand jury probe are ugly accusations. Of course, we must withhold final judgment until all the facts are in, but at first blush, it appears that this time Quattrone may be down for good.