What is the burden of proving that a search warrant was obtained without a warrant?

The defendant bears the initial burden of showing that police officers acted unlawfully. When the defendant shows that entry was made without a warrant, the burden shifts to the prosecution to prove that it was reasonable. This is usually done by showing exigent circumstances. If the prosecution fails to carry its burden, the defendant need do nothing more to be entitled to suppress primary evidence. (People v. Williams (1988) 45 Cal.3d 1268, 1300, 248 Cal.Rptr. 834, 756 P.2d 221.)

The trial court's role in a suppression motion is to make factual findings concerning the history of the events, to select the applicable rule of law, and to apply the law to the facts to establish whether or not there has been a constitutional violation. The trial court's factual findings are reviewed on appeal under the deferential substantial-evidence standard. Its selection of the governing legal principles and its application of those principles, however, are subject to the appellate court's independent review. (People v. Williams, supra, 45 Cal.3d 1268, 1301, 248 Cal.Rptr. 834, 756 P.2d 221.)