US prosecutors signalled a new aggressiveness in their pursuit of white-collar crime on Friday by revealing that they had used court-authorised wire taps in the investigation that led to the filing of insider trading charges against hedge fund manager Raj Rajaratnam and five other people.

Preet Bharara, US attorney in Manhattan, warned that the “same powerful investigative techniques that worked so successfully with mob and drug cartels” would also be used in white-collar probes. He said Friday’s case marked the first time wire taps had been used in a significant insider trading case.