One substantive question, directed at those who have read the short and readable opinion. On page 9, when the court notes that the use of radar might have dispelled the reasonable suspicion needed to justify the protective sweep, does it matter which side has the burden of proof to prove reasonable suspicion? If the government has the burden of proving reasonable suspicion, should the court treat the absence of information in the record on this point as not changing its otherwise-reached view that there is reasonable suspicion (as it does), or should that be treated as a potentially serious deficiency in getting to reasonable suspicion that the government has to overcome?
I’m not sure of the answer. We don’t normally encounter this question because we normally understand the uses and limits of investigatory tools. If the officer looked through the window and didn’t see any other people, for example, we could intuitively factor that into the reasonable suspicion inquiry without having to think about burdens of proof. I’m less sure what we’re supposed to do when the government use a suspicion-testing technological device with unknown capabilities. The opinion relies on the language from Buie that “the sweep lasts no longer than is necessary to dispel the reasonable suspicion of danger,” and thus asks whether there was evidence that the Doppler device “dispel[led]” the reasonable suspicion. But it’s not clear to me that this language from Buie applies here, as it was referring to evidence after reasonable suspicion was established and the entry was made rather than before.
My instinct is that the Tenth Circuit’s approach was correct here, as United States v. Arvizu, 534 U.S. 266 (2002), suggests that reasonable suspicion is a pretty holistic inquiry. So even if there were technical limits on the Doppler device, the officer wouldn’t be required to know them and carefully consider them in making a common-sense judgment about reasonable suspicion. But it’s an interesting question, I think.
UPDATE: I have added a sentence or two for completeness shortly after posting.