The Fourth Amendment may be implicated in obtaining physical evidence such as hair samples, fingernail scrapings, blood samples and other evidence from the person of an individual. Unlike physical appearance, writing, speaking, fingerprints, and measurements which are exposed to the public, the taking of evidence such as hair and blood samples creates greater concerns under the Fourth Amendment. Compare United States v. Wade, supra, with Schmerber v. California, 384 U.S. 757 (1966).
Obtaining physical evidence from a person involves a potential Fourth Amendment violation at two different levels--the "seizure" of the "person" necessary to bring him/her into contact with government agents, and the subsequent search for or seizure of the evidence. See United States v. Dionisio, 410 U.S. 1, 8 (1973); Schmerber v. California, supra. Even where there has been a lawful arrest, a subsequent search for physical evidence must comply with the requirements of the Fourth Amendment.