Federal criminal charges are an entirely different beast than state charges. Not only do federal prosecutions proceed at a much faster pace than state cases, but the typical federal case is much more complicated and the stakes are usually much higher. Federal prosecutors are more selective in deciding which cases should be formally charged. The cases selected for federal prosecution are frequently the result of multi-year investigations conducted by several different law enforcement agencies.
If you discover that you are under federal investigation, the importance of contacting an attorney immediately cannot be over-emphasized. Oftentimes the window of opportunity to work out the best possible resolution is prior to the filing of formal charges.