Credit Suisse First Boston (CSFB), one of the mightiest finance houses on Wall Street, has suspended a top banker as part of widening investigation into share offerings.

Until Monday, CSFB had stood by Frank Quattrone, head of its once-booming global technology group.

But the bank suspended him after learning that he may have destroyed key documents relating to a number of investigations into the firm.

CSFB is coming under regulatory pressure - primarily from the National Association of Securities Dealers (NASD) - over the way it allocated shares in some of the most popular flotations during the hi-tech boom of the late 1990s.

It is not clear whether Mr Quattrone's suspension was directly related to the NASD case; the firm only admitted that he was under suspicion over "document retention issues".

Red faces

The Quattrone case is the latest in a string of embarrassing probes into CSFB.

The bank has been sued in New York over allegations that its analysts were biased in the way they tipped shares.

When John Mack took over as chief executive in 2001, he promised to clear up the bank's wheeler-dealing reputation.

But although Mr Quattrone was already under investigation at that point, Mr Mack publicly supported him, and elevated him to the CSFB executive board.

CSFB, which was arguably the most successful Wall Street house during the 1990s boom, has suffered sharply since, thanks to its reliance on hi-tech and telecoms-related business.