"The Rapid Passenger Tracking solution basically uses facial recognition -- whether that's by a human, or a computer, or a combination of the two -- only in the very last step in our processing chain after we've reduced the problem to a manageable data set."

Using the 2005 London bombings as an example of how crucial quick detection is in subway crimes, Haddy says it took more than a week for investigators to manually locate video showing the key suspects at King's Cross station which subsequently proved critical to the investigation. The search of video data at King's Cross was a result of "somebody's hunch".

Based on various scenario tests in simulation environments created for the London Underground and other networks around the world, he believes the tracking software would be able to isolate video of the bombing suspects within minutes and have allowed investigators to examine complete journeys for suspects the same day.

In fact, it was the 2005 bombings that originally inspired Haddy to develop his system. He says he was sitting on a plane flying between London and New York when, instead of reading the usual airport novel, he began tapping out elaborate graph theory algorithms on his laptop.

The tracking software automatically discards video footage of passengers who are irrelevant to an investigation. This not only helps protect the privacy of those passengers not involved in a crime incident, but also helps deal with network bandwidth constraints by reducing the amount of video data that's needed to download or retrieve.