update:
Murder Suspect Has Witness: A MetroCard "
"The MetroCard, used when boarding New York City buses and entering subway stations, has a magnetic strip that records the amount of money or time left on the card. Centralized computers also store data on where and when the cards are used, retrieving the information from buses and subway turnstiles."
If you live in New York, you may have wondered if the MTA keeps a database of all metro card swipes. The answer is "yes". They can obviously export it to Excel rather easily too.