What is the test for a de facto arrest under the Fourth Amendment?

Defendant's de facto arrest must have been supported by probable cause in order to be reasonable under the Fourth Amendment. Probable cause is a fair probability"when the facts known to the arresting officer would lead a person of ordinary care and prudence to entertain an honest and strong suspicion that the person arrested is guilty of a crime. [Citations.]" (People v. Price (1991) 1 Cal.4th 324, 410.) In the present case, if the shotgun had already been located in defendant's bedroom, that would certainly have provided the sufficient probable cause to support the de facto arrest occasioned by defendant's transport to the police station and subsequent questioning. The record, however, is unclear on the timing of the events.