It started with suspicious trades by a retired seamstress in Croatia and grew to include a cast of low-level Wall Street professionals and an exotic dancer.

These sources said they did not know how many of the firms may have customer accounts where suspicious trades occurred.

In a letter to Congress on May 30, Mr. Aguirre said the S.E.C. was responding too slowly to concerns by stock exchange officials that Pequot had engaged in suspicious trades.

Unscrupulous insiders, with the cooperation of their brokers, could simply put together a plan that conformed to the suspicious trades, then date it before the fact.

The trade, sudden and to his mind suspicious, that had sent the right-hander from the Mets to the Blue Jays last Thursday.

And despite all the computer advances in monitoring the markets for suspicious trades, insider trading remains a crime that cannot be proved without the assistance of at least one of the culprits.

Kerviel is not thought to have profited personally from the suspicious trades.

Of these, 220 "included one or more suspicious trades executed through foreign institutions."

Over the weekend, the manager spotted some suspicious trades, further raising his concern, Mr. Bramble said.

The chief financial officer of Nortel Networks was forced to resign after the company said it had notified regulators of suspicious trades in his 401(k) retirement account.