"But there is not a Barney Fife defense to violation of the Fourth Amendment, either." Pamela Karlan, for the defendant, got off that good line in yesterday's oral argument in Herring v. United States, No. 07-513. On the whole though, she had a pretty rough time of it. Orin Kerr at VC thinks it's "a pretty clear win for the government."
The Question Presented is, "Whether the Fourth Amendment requires evidence found during a search incident to an arrest to be suppressed when the arresting officer conducted the arrest and search in sole reliance upon facially credible but erroneous information negligently provided by another law enforcement agent."
As Chief Justice Roberts notes at page 14, the question of the exclusionary remedy is separate from the question of a violation of the Fourth Amendment, so the nonexistence of a Barney Fife defense to violation is beside the point. In modern cases, the question of whether to extend the exclusionary remedy to a particular type of violation has been based on utilitarian cost v. benefit considerations. See Arizona v. Evans, 514 U.S. 1 (1995). At each point where that question has been the main focus, the decision has been against exclusion.
As the lawyers argued over whether exclusion should apply to all errors or just negligent ones or to isolated problems or systemic ones, Justice Scalia was concerned over how much litigation would be required to determine the facts needed for a decision. See pp. 16, 57. That is an important point. Criminal courts are overloaded to the point that most cases have to be plea-bargained down to less than the perp actually committed. Every additional litigation straw on the camel's back aggravates the problem.
Justice Kennedy asks at a couple of points if civil suits under 42 U.S.C. § 1983 aren't a better way to deal with the problem of pervasively sloppy record keeping on the currency of warrants. See pp. 31, 37. Justice Ginsburg doesn't seem convinced. See p. 53.
That last point brings us to the elephant in the living room -- the big issue everyone knows but doesn't want to talk about. If you want an "absolutely clear line," Justice Breyer (p. 35), here it is: Weeks v. United States, 232 U.S. 383 (1914) was wrongly decided. The Fourth Amendment had nothing to do with the admissibility of evidence in criminal trials in its first 122 years, and it does not today. It is a civil matter.