Whether an officer's mistake of fact in using excessive force is a legal or factual question for determining reasonableness at summary judgment, and whether deadly force can be deemed reasonable based on post-hoc facts or a broad constitutional interpretation

1. In a case alleging that an officer used excessive force based on a mistake of fact, is the reasonableness of the officer’s mistake a legal question for a court at summary judgment or a factual question for a jury? 2. May an officer’s use of deadly force be deemed reasonable as a matter of law based on facts that were not known to the officer at the time or based on a view that “[t]here is no constitutional … right that prevents an officer from using deadly force when faced with an apparently loaded weapon”? App. 14a.