CA1 seems to shift burden of proof to defendant to show that his detention was unreasonable because of a show of authority

The First Circuit seems to shift burden of proof to defendant to show that his detention was unreasonable because of a show of authority, rather than it being on the government that it was reasonable. United States v. Fields, 2016 U.S. App. LEXIS 8834 (1st Cir. May 13, 2016):

But the burden is on Fields to establish the show of authority that is the necessary predicate for his claimed Fourth Amendment violation. And under the totality of the circumstances test that we must apply, we do not on these facts see a basis for overturning the District Court’s conclusion that Fields failed to demonstrate that there was a show of authority at the time the four backup officers arrived on the scene — a conclusion, we add, that the District Court reached only after a thorough consideration of the testimony and evidence presented at the suppression hearing. We thus affirm the District Court’s decision to deny Fields’s motion to suppress on the basis that there was no show of authority and consequently no unlawful seizure at the time that Fields contends one occurred.