Is the allegation of prosecutorial vindictiveness in the context of an allegation of retaliation for the assertion of a procedural right?

Thurnhuber's allegations of prosecutorial vindictiveness, therefore, must rest on an improper motive other than retaliation for the assertion of a procedural right. It is Thurnhuber, however, who bears the burden of showing improper prosecutorial conduct sufficiently grave to overcome an otherwise proper conviction. See, e. g., United States v. Oaks, 527 F.2d 937, 940 (9th Cir. 1975), cert. denied, 426 U.S. 952, 96 S.Ct. 3177, 49 L.Ed.2d 1191 (1976); United States v. Scott, 521 F.2d 1188, 1195 (9th Cir. 1975), cert. denied, 424 U.S. 955, 96 S.Ct. 1431, 47 L.Ed.2d 361 (1976); United States v. Bennett, 539 F.2d 45, 54 (10th Cir.), cert. denied, 429 U.S. 925, 97 S.Ct. 327, 50 L.Ed.2d 293 (1976).