Most discussions of privacy and surveillance proceed from the assumption that digital records are harmful to those whose whereabouts, actions, statements and associations they preserve. A digital dossier may well be dangerous. Like DNA evidence, it can confirm suspicions of wrongdoing.

But the Supreme Court confirmation hearing for Kavanaugh provides a reminder of an often-overlooked aspect of the digital footprints we leave everywhere: Every form of surveillance can also supply an alibi. Like DNA, a digital record can protect the innocent as well as finger the guilty.

Defense lawyers already use cell-tower records to cast doubt on their clients’ presence at crime scenes. Such records, along with time-stamped digital photos, provided important exculpatory evidence in the infamous 2007 case in which Duke University lacrosse players were acquitted of rape.