Roomy Khan, one of the first cooperating witnesses who helped build the US government's case against convicted hedge-fund manager Raj Rajaratnam, was sentenced to one year in prison on Thursday.

Most key witnesses in the wide-ranging probe of insider trading have received probation. But Khan, who began to work with investigators six years ago, lied to the Federal Bureau of Investigation early in her cooperation about her own criminal conduct, according to the government, hurting her chances of avoiding prison.