What is the test for a motion to suppress for abuse of power?

We review a district court's decision whether to conduct an evidentiary hearing on a motion to suppress for abuse of discretion. United States v. Mejia, 953 F.2d 461, 465 (9th Cir.1991), cert. denied, 112 S.Ct.1983 (1992). We review de novo the district court's ultimate conclusion as to the lawfulness of a seizure, but review its underlying factual findings for clear error. Id. at 464.