What is the test for police contact with a potential criminal suspect?

The police contact at issue in Florida v. J.L., supra, 529 U.S. 266, 120 S.Ct. 1375, 146 L.Ed.2d 254, was a detention. Therefore, officers were required to "reasonably conclude in light of [their] experience that criminal activity may be afoot...." (Id. at pp. 269-270, 120 S.Ct. 1375 quoting Terry v. Ohio (1968) 392 U.S. 1, 20, 88 S.Ct. 1868, 20 L.Ed.2d 889.) The reliability of the tip is essential in this context because "[t]he reasonableness of official suspicion must be measured by what the officers knew before they conducted their search." (Id. at p. 271, 120 S.Ct. 1375.)