[This is a guest commentary by Richard Byrd, a retired Northern Virginia attorney residing in New England.]  

            I read your blog entry regarding the Grim Sleeper case. Such a use of high technology for surveying many innocent people to perhaps catch one criminal was explored deeply in the 5-4 decision in Kyllo v. United States, 533 U.S. 27 (2001). [Majority opinion] [Dissent].  

            The controversy was about the use of a thermal-imaging device to scan residences for the heat being emitted by the house itself. Many people growing marijuana use high intensity heat lamps to grow the plants faster. A detective used the heat-seeker to drive down residential streets looking for "hot-spots." He found that Danny Kyllo had a very hot garage. The detective got a warrant on this basis and a search revealed over 100 marijuana plants being cultivated in the garage. Kyllo moved to suppress the evidence, but the district court denied his motion. Kyllo entered a conditional guilty plea and appealed his case to the 9th Circuit Court and ultimately to the Supreme Court.  
            The district court found the imager was non-intrusive, since only a crude visual image of heat from the outside of the house was revealed. The imaging did not reveal any activity in the house, and so no intimate details had of the residents were shown by the scan. The 9th Circuit Court affirmed the district court that Kyllo's rights had not been denied because of an unconstitutional search.
            The U.S. Supreme Court found that to “explore the details of the home that would previously have been unknowable without physical intrusion, the surveillance is a 'search' and was unreasonable without a warrant.”

            In the majority opinion, Justice Scalia said:

  • “The present case involves officers on a public street engaged in more than naked-eye surveillance of a home. We have previously reserved judgment as to how much technological enhancement of ordinary perception from such a vantage point, if any, is too much. While we upheld enhanced aerial photography of an industrial complex in Dow Chemical, we noted that we found 'it important that this is not an area immediately adjacent to a private home, where privacy expectations are most heightened.' [Dow Chemical Co. v. United States, 476 U. S. 227, 234-235, 239] …
  • “We have said that the Fourth Amendment draws 'a firm line at the entrance to the house' … That line, we think, must be not only firm but also bright—which requires clear specification of those methods of surveillance that require a warrant. While it is certainly possible to conclude from the videotape of the thermal imaging that occurred in this case that no 'significant' compromise of the home-owner's privacy has occurred, we must take the long view, from the original meaning of the Fourth Amendment forward …

  • “Where, as here, the Government uses a device that is not in general public use, to explore details of the home that would previously have been unknowable without physical intrusion, the surveillance is a 'search' and is presumptively unreasonable without a warrant.

  • “Since we hold the Thermovision imaging to have been an unlawful search, it will remain for the district court to determine whether, without the evidence it provided, the search warrant issued in this case was supported by probable cause — and if not, whether there is any other basis for supporting admission of the evidence that the search pursuant to the warrant produced.”

            There certainly seems to me to be a similarity between cruising innocent people for heat signals and cruising innocent people for DNA matches. The technical distinction between the cases may be in the comparison between the detective tricking the father into giving up some DNA compared to just simply taking the heat signatures. In any case, modern technology is presenting difficult challenges for the eternal debate between privacy and law enforcement.

[Editor's Note: For a law review article on the adaptation of Fourth Amendment law to new technology, see Orin S. Kerr, "An Equilibrium-Adjustment Theory of the Fourth Amendment" 125 Harv. L. Rev. 476 (2011).]