What is the legal test for a search and/or seizure?

It is well-settled that the People, faced with a constitutional challenge to a search and/or seizure, have the burden of going forward with evidence to show the legality of the police conduct in the first instance. People v. Berrios, 28 N.Y.2d 361, 367, 321 N.Y.S.2d 884, 270 N.E.2d 709 (1971). It is the defendant, however, who bears the ultimate burden of proving, by a preponderance of the evidence, that the evidence seized should not be used against him. People v. Thomas, 291 A.D.2d 462 (2nd Dept.2002). Here, the People have met their burden of going forward with evidence to show the legality of the police conduct and defendant has not met his burden to establish that the evidence should not be used against him.