The Fourth Amendment protects people and property from “unreasonable searches and seizures.” That means cops can’t just stop any vehicle they want on the off chance that the driver is Jesse Pinkman with a load of meth. Courts require a “reasonable suspicion” that the specific person being stopped has done something criminal. The courts have also held that the mere fact that a police officer has gotten (or claims to have gotten) a tip does not create by itself “reasonable suspicion.” The tip must either be from a known and credible source, or, if anonymous, must itself contain “indicia of reliability,” such as detailed predictions of what the suspect will do or other information to suggest that the secret tipster has more than malice in mind. The call in Navarette described an incident of dangerous driving and gave the car’s license number and direction of travel. That by itself might not be enough.

As it reached the Supreme Court, thus, Navarette was a case about anonymous 911 callers. But the 911 call in Navarette was not, in what for lack of a better word I will call fact, anonymous at all.

According to the record in the case, the caller gave the 911 operator her name. But at the outset of the trial, the prosecutor summoned the wrong 911 operator and wasn’t able to get the actual recording of the call into evidence. The case had to progress as if the call had been anonymous.

Well, you might say, no harm, no foul. It’s an important issue and the Court needed to decide it. But consider that Thomas’s opinion turned almost entirely on factual speculations. (Thomas was aware of the record below, and references it obliquely in his opinion.) Reasonable suspicion depends on “the factual and practical considerations of everyday life on which reason-able and prudent men, not legal technicians, act,” Thomas wrote, quoting case law. In this case, the decision to stop seemed reasonable.

Why? Some 911 systems, Thomas wrote, have technological “features that allow for identifying and tracing callers, and thus provide some safeguards against making false reports with immunity.” So, since a 911 call may not be anonymous at all, “a reasonable officer could conclude that a false tipster would think twice before using such a system.”

Scalia (writing for himself and Justices Ruth Bader Ginsburg, Sonia Sotomayor, and Elena Kagan) noted an amicus brief from the National Association of Criminal Defense Lawyers suggesting that 911 systemsc can be used for false tips without fear of detection. He then wrote, “the present case surely suggests that amici are right—since we know neither the identity of the tipster nor even the county from which the call was made. But assuming the [majority] is right about the ease of identifying 911 callers, it proves absolutely nothing in the present case unless the anonymous caller was aware of that fact.” (This isn’t a second Scalia-mistake story; references in the opinion make clear that Scalia also knew the record below.)