Defense lawyers for a hedge fund billionaire charged with insider trading Monday accused the government of “gaming the system” by failing to advise the judge who approved the wiretaps that much of the evidence had been gathered in other ways, making the electronic surveillance unnecessary.

On the critical issue of whether there were no adequate alternatives to wiretaps, a lawyer for Raj Rajaratnam, the founder of the Galleon Group, told Southern District Judge Richard J. Holwell that during a yearlong joint investigation, the Securities and Exchange Commission and federal prosecutors had built a “conventional” insider trading case against Rajaratnam using “conventional” techniques.