The Transit Trail: Using MetroCards to Solve Crime (and why we know where you are right now…)

Since the MTA completed its transition from token to MetroCard in 1997, the electronic fare cards have been used on many occasions to help solve criminal cases. In 2001, a transit worker named Christopher Stewart was accused of stabbing an ex-girlfriend to death in Staten Island. His alibi placed him on a ferry to Manhattan, but the trail left by his MetroCard told a different story—he’d swiped it on a bus near the scene of the murder twelve minutes after the crime took place. The new evidence won the case for the prosecution, and Stewart was convicted of second-degree murder.

MetroCards have been used to exonerate as well as condemn. In 1998, for example, a Brooklyn high-school student filed a federal civil rights case after being arrested for allegedly hopping a turnstile. The student had been on his way to the library to work on a school project, and ended up spending nineteen hours in custody instead. Two years after the incident, electronic records from the MTA showed that the kid had, in fact, swiped his card right before being picked up by the cops.

So, how is it possible to trace one MetroCard out of five million? The third track (see Monday's Post) on a MetroCard is encoded with a unique serial number when the card is manufactured. When a MetroCard is swiped at a station or on a bus, the data on the card is both read and rewritten by a magnetic read/write head (see tomorrow’s post), and all data from the transaction is conveyed to the Automatic Fare Collection Database—a central computer database where all electronic transit histories are stored.

What does this mean for you, assuming you aren’t a public-transit-reliant criminal? If you buy your MetroCards in cash, your transit history trail can be traced only for as far back as the card in your wallet goes. If, on the other hand, you use a credit or debit card each time you purchase a new transit ticket, the Automatic Fare Collection Database knows who you are and where you’ve been going since you first stepped through a turnstile.