Potential defenses to a case plaintiff was arrested for do not nullify the probable cause. Chiaverini v. City of Napoleon, 2023 U.S. App. LEXIS 865 (6th Cir. Jan. 11, 2023):
Simply put, Chiaverini’s potential defenses to a crime don’t affect the initial probable cause determination. Ideally, perhaps, officers investigating allegations like these might inquire into obvious explanations or defenses that a prosecutor can consider. But nothing required the police to investigate Chiaverini’s affirmative defense. Fridley, 291 F.3d at 873 (“[I]t is not a routine part of the prearrest investigation for police officers to inquire into affirmative defenses.”) Although “innocent explanations . . . may exist,” they don’t “render the  determination of probable cause invalid.” United States v. Martin, 289 F.3d 392, 400 (6th Cir. 2002); see United States v. Terry, 522 F.3d 645, 648-49 (6th Cir. 2008) (explaining that probable cause “does not require ‘near certainty,’ only a ‘fair probability'” (citation omitted)). And we have explained that “the Fourth Amendment does not require that a police officer know a crime has occurred at the time the officer arrests or searches a suspect.” United States v. Strickland, 144 F.3d 412, 415 (6th Cir. 1998).