However, if the police arrest a suspect, they can still find their transit history by examining any card they have in their possession, regardless of how it was bought. So if you plan on committing a crime (or just don't want to be tracked), you should buy some low-denomination MetroCards with cash at random locations and discard them immediately after passing the turnstile. And you should leave your cell phone at home too, since that also leaves a trail of where you've been. Don't drive to the scene of the crime either, since you might be identified by one of the NYPD's license plate scanners (or a red-light or speeding camera, or an E-ZPass toll scanner). And if you manage to avoid all those pitfalls, you might still get identified by one of the thousands of surveillance cameras around NYC. It's getting very hard to travel anonymously in NYC.