'Ever since its inception, the rule excluding evidence seized in violation of the Fourth Amendment has been recognized as a principal mode of discouraging lawless police conduct. . . . [W]ithout it the constitutional guarantee against unreasonable searches and seizures would be a mere `form of words.'' Terry v. Ohio, 392 U.S. 1, 12 (1968), quoting Mapp v. Ohio, 367 U.S. 643, 655 (1961). The occasional suppression of illegally obtained yet probative evidence has long been considered a necessary cost of preserving overriding constitutional values: '[T]here is nothing new in the realization that the Constitution sometimes insulates the criminality of a few in order to protect the privacy of us all.' Arizona v. Hicks, 480 U.S. 321, 329 (1987). The Supreme Court has carved out exceptions to the exclusionary rule where the introduction of reliable and probative evidence would significantly further the truth-seeking function of a criminal trial and the likelihood that admissibility of such evidence would encourage police misconduct is but a 'speculative possibility.' Harris v. New York, 401 U.S. 222, 225 (1971). See generally Illinois v. Krull, 480 U.S. 340, 347 (1987) (when evaluating proposed exceptions to the exclusionary rule, the Court 'has ...