What is the burden of proving in a suppression hearing?

We disagree. It would ordinarily be impossible to make an investigation, have a hearing, and permit the introduction of evidence and cross-examination, with some resultant finding based upon whatever standard of proof might be appropriate, see, e. g., Lego v. Twomey, 404 U.S. 477, 92 S.Ct. 619, 30 L.Ed.2d 618 (1972) (upholding the use of the preponderance-of-evidence standard as the burden of proof in a suppression hearing re the voluntariness of a confession), meanwhile suspending the trial in question. It is simply impracticable in the situation of the killing of a key witness to reach any well-founded determination about the true course of events in an hour, a day, a week, or even a month.