The US Department of Justice has an excellent site devoted to requesting federal public records through the Freedom of Information Act. 

From www.usdoj.gov Freedom of Information Act site:

Like all federal agencies, the Department of Justice (DOJ) generally is required under the Freedom of Information Act (FOIA) to disclose records requested in writing by any person. However, agencies may withhold information pursuant to nine exemptions and three exclusions contained in the statute. The FOIA applies only to federal agencies and does not create a right of access to records held by Congress, the courts, or by state or local government agencies. Each state has its own public access laws that should be consulted for access to state and local records.

The US DOJ FOIA site contains reference guides and principal FOIA contacts for major government agencies.  You can access the USDOJ FOIA site at Freedom of Information Act .