Yesterday I noted the pattern of abuses revealed by complaints against U.S. Border Patrol agents that the ACLU of Arizona obtained by suing the Department of Homeland Security under the Freedom of Information Act. The ACLU's report on those complaints and other documents it obtained as a result of the lawsuit is now available on its website (where you can also read some of the documents). In addition to arbitrary detentions and fruitless, dog-authorized searches at internal immigration checkpoints, the report discusses unjustified stops by "roving patrol" vehicles inside (and sometimes outside) the 100-mile border zone that the Border Patrol claims as its turf. The ACLU says "these documents show that Border Patrol's extra-constitutional police practices often amount to a de facto policy of 'stop and frisk' for border residents."
The incidents described in the report include motorists whose cellphones were confiscated when they attempted to record their checkpoint stops; people who were threatened with stun guns for daring to question agents' authority to detain, question, and search them; motorists who discovered property damaged or missing after searches justified by purported canine alerts; a man pulled over by Border Patrol agents seven times in one year while commuting to work; "a school bus that has been detained 'dozens of times' for secondary inspections while students are forced to stand in 100-degree heat and submit to searches of personal belongings"; a woman driving at night with her 4-year-old daughter on Interstate 10 who was tailed and stopped by a roving patrol car for no apparent reason, then interrogated and searched; and a family pulled over as they were leaving their home by a Border Patrol agent who said "I don't have to tell you" the reason for the stop.
The 142 complaints reviewed by the ACLU, which represent just a small sample of complaints against Border Patrol agents, include "44 allegations of false canine alerts resulting in prolonged detentions and/or searches of individuals who did nothing wrong and were ultimately released." In such cases, it is impossible to say whether the dog actually alerted and, if it did, whether the alert was caused by distracting odors, its handler's conscious or subconscious cues, or (as the government usually argues) imperceptible traces of contraband the vehicle once carried. But given the Supreme Court's rulings in this area, a cop with a dog in practice has the power to search any vehicle he wants. Since the Border Patrol does not keep track of fruitless searches, we have no idea how accurate its dogs are in the field, but even a well-trained dog is apt to generate many more false positives than true positives.
The prominence of drug-sniffing dogs in these encounters belies the claim that catching illegal immigrants is the main function of the checkpoints. The ACLU notes that checkpoints account for less than 1 percent of apprehensions in the Tucson and Yuma sectors. In 2013 Yuma Sector checkpoints caught just 197 deportable aliens while arresting 1,535 citizens or legal residents, mainly on drug charges. Similarly, The New York Times reports that in fiscal year 2013 checkpoints accounted for 14 percent of marijuana seized near the borders with Mexico and Canada but only 2 percent of unauthorized immigrants apprehended.
Although it's pretty clear that enforcing drug prohibition is the main function of the checkpoints, the Supreme Court has explicitly rejected that goal as a justification for random traffic stops. When the Court upheld the Border Patrol's checkpoints in the 1976 case U.S. v. Martinez-Fuerte, the justification was enforcement of immigration law. As Alex Kozinski, a judge on the U.S. Court of Appeals for the 9th Circuit, observed in a 1993 case quoted by the ACLU, "There's reason to suspect the agents working these checkpoints are looking for more than illegal aliens." He added that "if this is true, it subverts the rationale of Martinez-Fuerte and turns a legitimate administrative search into a massive violation of the Fourth Amendment."