What is the test for holding an evidentiary hearing for abuse of power?

We review a district court's decision to conduct an evidentiary hearing for an abuse of discretion. United States v. Mejia, 953 F.2d 461, 465 (9th Cir.1991), cert. denied, --- U.S. ----, 112 S.Ct. 1983, 118 L.Ed.2d 581 (1992). "An evidentiary hearing on a motion to suppress ordinarily is required if the moving papers are sufficiently definite, specific, detailed, and nonconjectural to enable to the court to conclude that contested issues of fact" going to the legality of the government's conduct are in issue. United States v. Walczak, 783 F.2d 852, 857 (9th Cir.1986). Evidentiary hearings on motions to suppress on voluntariness grounds are required where "substantial facts are in dispute." United States v. Jenkins, 785 F.2d 1387, 1394 (9th Cir.), cert. denied, 479 U.S. 855, 107 S.Ct. 192, 93 L.Ed.2d 125 (1986).