The Reasonableness of Probable Cause

[A]lthough I thought that probable cause existed ("probable cause" meaning that the proposition has to be more likely than not, or if quantified, a 51% likelihood), I thought our United States Attorney's Office . . . [is] regularly requiring much more than probable cause before approving affidavits, (maybe, if quantified, 75%-80% probability and sometimes even higher) . . . .1 I. Introduction Nearly a month before the September 11 attacks, FBI agents in Minneapolis arrested Zacarias Moussaoui on an immigration overstay violation. His perplexing determination to fly, or simply steer, a jumbo jet, combined with his links to radical Muslim fundamentalists, sparked concern in the FBI's Minneapolis field office. Moussaoui's claims, when questioned, to being "just a businessman," proved specious, and agents were eager to confirm, or allay, their relatively inchoate concerns by searching Moussaoui's laptop computer. Yet Moussaoui refused to consent. Was there probable cause to obtain a warrant?2 Coleen M. Rowley, the Chief Division Counsel of the FBI's Minneapolis office, thought so.3 As reflected in the quotation that introduces this Article, she placed the likelihood of criminal activity at greater than fifty percent. The established practice in the federal system, however, requires law enforcement officers to secure approval for warrant applications from a prosecutor, and in Rowley's estimation, the U.S. Attorney's Office in Minneapolis required showings akin to a "clear and convincing" evidentiary IMAGE FORMULA13 standard. In late August, Rowley instead tried to convince FBI headquarters to approve a warrant under the Foreign Intelligence Surveillance Act. But headquarters balked, despite the persistent, and increasingly frantic, efforts on the part of Rowley and others in the Minneapolis office. Months after the September 11 attacks, Rowley sent FBI Director Robert Mueller a memo excoriating headquarters for its refusal to approve the warrant application.4 Among the important issues raised in the Rowley Memorandum5 is the meaning of probable cause, that elusive and perhaps hopelessly indeterminate constitutional standard for the issuance of law enforcement warrants.6 For her arguments on this point and several others, Rowley was hailed, after the memo's publication, as "[t]he blunt Midwesterner" ultimately vindicated in her struggle with Washington bureaucrats. And yet, was she vindicated? The fact that a crime eventually occurs does not mean that probable cause existed at every antecedent point in time. If a police officer sees four former felons gathering in the back room of a bar, probable cause does not then exist to arrest them and search their homes. Even if it emerges that a bank robbery could have been prevented had warrants been issued, hindsight bias should not cloud an assessment of probable cause. Perhaps sensing the direction and violence of the political winds, Director Mueller declined to make this point forcefully in response to the Rowley Memorandum. In fact, he joined the chorus of fulsome praise. But in the midst of his commendation of the "aggressive[]" efforts of the Minneapolis field office, Mueller struck this discordant note: "The attorneys back at the FBI determined that there was insufficient probable cause for a [warrant], which appears to be an accurate decision."8 In effect, then, Mueller seemed to suggest, if ever so tactfully, that with respect to one of the central points of her memo, Rowley was wrong.9 IMAGE FORMULA15 The layperson may be excused for finding all of this bewildering. We are to understand that the FBI acted commendably in investigating Moussaoui, that there was a nontrivial likelihood that he was engaged in criminal activity of the gravest sort, and that the search the FBI proposed to conduct of Moussaoui's laptop was narrowly tailored to address its concerns. …