What are the grounds for dismissal of an indictment for conspiracy to pervert the course of justice?

The defendants' various other arguments in support of dismissal of the indictment either are meritless or must be rejected at this stage for the reason that they would require factual findings that have not been made. For instance, having lost their claim in the district court that the indictment is dismissible under the Speedy Trial Act, 18 U.S.C. Secs. 3161, et seq., a claim which is not advanced on this appeal, defendants here press for dismissal under F.R.Cr.P. 48(b), urging that the government's pre-indictment delay was purposeful and unnecessary. See Barker v. Wingo, 407 U.S. 514, 92 S.Ct. 2182, 33 L.Ed.2d 101 (1972).