Has your friend been arraigned in federal court? If he has not been arraigned, you might contact the local Federal Public Defenders office. .
If he has been arraigned in federal court, the question of whether the magistrate will release him relates to factors that are found in the federal statutes. 18 USC 3142. Even in a co-defendant case, that is two or more people have been charged, there might be different decisions as to whether to release the defendant from custody.
Its not really possible to know what the issue is with your friends case, but you might get better information by contacting a criminal defense attorney with federal experience. I hope you can get a better answer.
This response is given for informational purposes only.
My colleague has given you a concise and accurate overview of the situation, and all I would add is that a number of factors can differentiate between co-defendants, such that one might be released and the other held on the same charges. The co-defendant could be cooperating with the government or your friend might have a criminal history or other status (e.g. hold from another jurisdiction, immigration issues, etc.) which might cause him to be held.
Overall, the best move for your friend is to sit down with an attorney, figure out where he stands in the case and take it from there.
I assume that your friend is in federal custody, since the fraud crimes you mention are federal crimes. If so, the following rules apply:
1. Under Rule 5.1(c) of the Federal Rules of Criminal Procedure, your friend has the right to a "preliminary hearing" within 14 days of his "initial appearance" if he is incarcerated on a complaint and 21 days if he has been released.
2. Under the Speedy Trial Act, specifically Section 3161(b) of Title 18 of the United States Code, the government has 30 days to charge your friend by indictment or information after he has been arrested or served with a summons. However, because the charges are felonies, the government cannot use an information (which does not require a grand jury) unless your friend waives (gives up the right to) indictment.