In short, the answer is to file a motion to compel. As part of that motion, you must demonstrate that you have first complied with Touhy regulations — i.e., served the correct person with the correct document. Failure to do so will require the district court to deny the motion: “Our record shows no effort by defendant to submit the affidavit or statement summarizing the testimony desired so that the Department could consider the request and determine whether to grant permission for the testimony…” so there was no “error in the court’s refusal to require testimony by the [employee].” United States v. Allen, 554 F.2d 398, 406 (10th Cir. 1977). Only by showing that you have complied with these procedures at the outset will the court be in a position to determine whether it “should have rejected a refusal by the Department due to the constitutional guarantees of the Fifth and Sixth Amendments.” Id. at 407.
Assuming you have demonstrated compliance with Touhy’s initial requirements, your motion to compel must also show that the evidence sought by the subpoena is material to your defense. See United States v. Rivera, 412 F.3d 562, 569 (4th Cir. 2005). This is the same standard that you had to satisfy to get the subpoena from the district court in the first place under Federal Rule of Criminal Procedure 17, so this should not be too tall of a hurdle.
If the department refuses your request outright, you should also make an argument under the Administrative Procedures Act, 5 U.S.C. §§ 701-706. Under the Act, federal courts have the authority to set aside any agency decision that is “arbitrary, capricious, an abuse of discretion,” or otherwise unlawful, including one that violates a “constitutional right, power, privilege, or immunity.” 5 U.S.C. § 706(2)(A)-(b). If the court concludes that the agency’s refusal meets any of these definitions, then it may “compel agency action unlawfully withheld… .” 5 U.S.C. § 706(1). These provisions allow you to incorporate your most powerful arguments — your client’s Fifth Amendment right to due process and Sixth Amendment right to compulsory process — directly into your statutory argument.
Complying with Touhy may seem intimidating at first blush. No one relishes paging through CFRs and attempting to decipher them. But they are not as complicated as they might appear. All you must do is write a letter, explain why you want a witness or document, wait for the letter to be ignored or refused, and then draft a motion to compel. As long as you’ve written the right letter and sent it to the right person, a court will rarely deny a request for evidence that is material to your defense.