I had criticized the 8th Circuit's panel decision in United States v. Kattaria here, back in October 2007, and today the en banc court handed down a new decision that allows the evidence without reaching the issue of whether the police can get a "reasonable suspicion warrant" to use an imaging device (effectively removing the panel's holding from the books).

  Chief Judge Loken, the author of the original panel decision, adds in a concurrence that partly sticks to his guns from the original panel holding but partly would amend it. Loken argues that the relevant Supreme Court precedents should be read relatively narrowly in a way that leaves open whether a lower standard than probable cause is allowed. He then writes:

On further reflection, I have concluded that the panel was unwise to borrow the concept of "reasonable suspicion" to reflect the quantum of probable cause that should be required in this situation. Reasonable suspicion is not focused to the task at hand, and it has never been applied to the warrant-issuing process. Rather, the question for the issuing magistrate (and reviewing courts) when considering an application like Agent Perry's initial warrant affidavit should be whether there is probable cause to believe that search of specific property -- the heat being emitted from a home -- in a specific manner -- by exterior thermal imaging -- for purely investigative purposes will uncover evidence of on-going criminal activity. Utility records showing abnormally high electric power usage are strong evidence supporting such an application but, without more, are unlikely to establish probable cause because of the many innocent uses of electricity. Cf. United States v. Olson, 21 F.3d 847, 850 (8th Cir.), cert. denied, 513 U.S. 888 (1994). But the "something more" should simply be enough particularized suspicion to justify the minimal intrusion caused by the exterior thermal imaging of heat emissions, without regard to whether there is probable cause to issue a warrant to conduct a full physical search.

  I'm not sure I understand this. On one hand, the standard for probable cause is probable cause to believe that the actual search that will be conducted will uncover the evidence described in the warrant based on the actual place that will be searched. As a result, the normal probable cause standard to justify use of a thermal imaging device should be what Loken describes in the middle of the paragraph above: "probable cause to believe that search of specific property -- the heat being emitted from a home -- in a specific manner -- by exterior thermal imaging -- for purely investigative purposes will uncover evidence of on-going criminal activity."

  But I'm not sure I follow the idea of permitting a warrant based on "enough particularized suspicion to justify the minimal intrusion caused by the exterior thermal imaging of heat emissions, without regard to whether there is probable cause to issue a warrant to conduct a full physical search." Probable cause to issue a warrant to conduct a full physical search would mean probable cause to believe that a full physical search would provide the evidence described in the warrant. That won't necessarily be the same as PC to use the imaging device, of course. But it won't necessarily be a harder standard to meet, either: It depends on the investigation and what the police know, and it could be easier or hard to meet depending on the facts. To the extent Judge Loken would want courts to apply a lower standard of probable cause, one that factors in the minimial intrusion of imaging devices relative to full physical searches, I don't think the Fourth Amendment allows it.