Three days before Spain’s general elections in 2004 a series of bombs exploded on crowded Madrid commuter trains, killing almost 200 people.

The Spanish authorities found a plastic bag a few blocks away from one of the bomb sites with a single, incomplete fingerprint.

This was the trace linked to a man living 9000 kms away, a US Attorney in Oregon by the name of Brandon Mayfield.

We’ve been told that every fingerprint is unique to every finger, but what if this is the wrong question to ask?

Forensic Science was founded on the principle that ‘every contact leaves a trace’ but history shows we can’t always rely on one trace alone.