After weeks of speculation on Wall Street, prosecutors brought a fresh round of insider trading charges on Thursday that left no doubt they were aiming at hedge funds and the networks of market gossip that are endemic on trading floors....

in the latest criminal complaints, prosecutors described a network that used prepaid cellphones to avoid detection, and that was pierced in part through surveillance and wiretaps.

One law enforcement official, speaking on condition of anonymity because the investigation is continuing, said the authorities expected to make more arrests in the coming weeks. The investigation is part of a broad Federal Bureau of Investigation push into crimes related to hedge funds, including the addition of a third securities fraud unit in New York, the official said.

And for the first time, the authorities hinted that they might be brushing against the pinnacle of the hedge fund world, S.A.C. Capital Management, a $12 billion Connecticut fund company.