What is the burden of proving that a showup procedure is unduly suggestive and subject to suppression?

While the defendant bears the ultimate burden of proving that a showup procedure is unduly suggestive and subject to suppression, the burden is on the People first to produce evidence validating the admission of such evidence. Initially, the People must demonstrate that the showup was reasonable under the circumstances. The People also have the burden of producing some evidence relating to the showup itself, in order to demonstrate that the procedure was not unduly suggestive... the People have the initial burden of going forward to establish the reasonableness of the police conduct and the lack of any undue suggestiveness in a pretrial identification procedure'[emphasis added]; see also People v. Riley, 70 NY2d 523, 531.