Mr Ezra had worked for the bank since 1987. Yesterday his solicitors said: "Mr Ezra has today resigned from his position as derivatives trader and vice-president of CSFB with immediate effect. He wishes to make it clear that he has at all times endeavoured to act in the best interests of CSFB.
"He will continue to co- operate to the best of his ability with all further inquiries regarding these matters."
The allegations of improper trading focus on Mr Archer's dealings on the Swedish stock exchange. Both the bank and the stock exchange are carrying out investigations and it is understood that a number of deals are being investigated by Swedish bank authorities and Britain's Securities and Futures Authority. The Swedish stock exchange is expected to complete its inquiry next week.
At the heart of the investigations are claims that Mr Archer, 24, aggressively sold shares in wood pulp company Stora, one of Sweden's biggest firms, in a bid to drive down the value of the Stockholm market index - the Swedish equivalent of the FTSE-100.
It is said he planned to make profits then by trading in the futures market - a complex system of gambling on the future value of shares, commodities and even whole stock markets.
Mr Ezra and Mr Crasanti were not involved in the deals, which took place in December, but as Mr Archer's bosses they were suspended pending the bank's investigation into how he was supervised.
Mr Ezra was unavailable for comment yesterday.