Fourth Amendment Doesn't Protect Spit on the Sidewalk:
Facts: Rape suspect walking on a street spits on the sidewalk. An investigator is following the suspect, and he collects the spit; a DNA test proves a match. Holding: No Fourth Amendment violation. Analysis:
[A]lthough the defendant had a reasonable expectation of privacy in his saliva (and other bodily fluids), see Matter of Lavigne, 418 Mass. 831, 835-836, 641 N.E.2d 1328 (1994); Jansen, petitioner, 444 Mass. 112, 120-121, 826 N.E.2d 186 (2005), when he expectorated on to a public street and did not retrieve the fluid, he voluntarily abandoned that protection; he assumed the risk of the public witnessing his action and thereafter taking possession of his bodily fluids. See Commonwealth v. Ewing, 67 Mass.App.Ct. 531, 540, 854 N.E.2d 993 (no expectation of privacy in cigarette butts abandoned as trash in interview room), further appellate review granted, 447 Mass. 1113, 857 N.E.2d 1094 (2006). See also Commonwealth v. Pratt, 407 Mass. 647, 660-661, 555 N.E.2d 559 (1990) (observations and inspections occurring after items deposited in public places generally fail to intrude upon reasonable expectation of privacy); Commonwealth v. Nutile, 31 Mass.App.Ct. 614, 619, 582 N.E.2d 547 (1991) (no reasonable expectation of privacy in drugs voluntarily thrown from vehicle); Commonwealth v. Wedderburn, 36 Mass.App.Ct. 558, 564, 633 N.E.2d 1058 (1994) (no reasonable expectation of privacy in drugs dropped on ground during police surveillance).

Here, the motion judge found that the location where the defendant spat was a public street, a place freely accessible to others. See Krisco Corp., 421 Mass. at 42-44, 653 N.E.2d 579. See also Commonwealth v. Pratt, supra (no reasonable expectation of privacy in trash left on curb); Commonwealth v. Bloom, 18 Mass.App.Ct. 951, 952, 468 N.E.2d 667 (1984) (defendant had no reasonable expectation of privacy in open area of public restroom). Moreover, there is no indication that the defendant took affirmative action to recover the saliva once it had left his mouth. In Bly, supra at 490-491, 862 N.E.2d 341, the defendant did not attempt to retrieve the cigarette butts when leaving the interview room, nor did he request to go back and collect them. The court held that Bly's "wholesale failure to manifest any expectation of privacy in the items whatsoever" compelled the "conclusion that [he] had no subjective expectation of privacy." Id. at 491, 862 N.E.2d 341. See Ewing, supra (defendant made no attempt to take cigarette butts when leaving interview room). Contrast Krisco Corp., supra at 45, 653 N.E.2d 579 (discussing affirmative steps taken by defendant to protect dumpster from public access). Thus, where the defendant here voluntarily abandoned his saliva onto a public street, the investigator (whether deemed to be functioning in a private capacity or as a State actor) did not infringe on any reasonable expectation of privacy when he recovered the spittle from the street.
Commonwealth v. Cabral, 69 Mass.App.Ct. 68, 2007 WL 1413143 (Mass. App. Ct. May 16, 2007).

  UPDATE: Elizabeth Joh had an interesting article on this very topic in the Northwestern University Law Review. You can download it here.