The authorities are now looking for anything that might have been part of the explosive devices - bits of metal or sharp objects that they might be able to trace back to its owner or owners.

BBC: Forensics investigators decode the Boston bombings

He thinks the financial services industry should create the identifier at the time of origination rather than work with closing and settlement records and then relying on data vendors such as Bloomberg or Reuters to trace back the instruments.

FORBES: Lehman, Lithium and Lettuce -- The Need for Unique Identifiers in Finance

"I've got lots of examples from research where college students and older say, 'I feel uncomfortable in a certain situation, and I trace it back to news or movie, ' " she said.

CNN: Terrorism, kidnapping among top fears for today's youth

Often, when I talk to people about why they decide to make a difference, why they become a part of an organization, why did they became passionate about something, they tend to trace it back to a book or a song or a movie.

UNESCO: Biodiversity Initiative

The "arrow of time" is based on the notion that it is possible to use data from modern languages to trace their origins back 10, 000 years or even further.

WSJ: Study Points to a Single, Original Language for All Humans

If they can pick up fibres or fingerprints from a crime scene, they can trace it back to the year, make, model of the car that the fibre came from and the thumb that left the fingerprint.

BBC

The police marks are used to trace bottles used in crime, or found with underage drinkers, back to the stores from which they were bought.

BBC: Glasgow & West Scotland

It can takes weeks or even months, if law enforcement is lucky, to trace a gun back to its origin.

CNN: Why new laws could miss America's bigger gun problem

Talk to any CEO or other successful person, and odds are he or she can trace the lessons they learned about teamwork, fair play, leadership and overcoming challenges back to Little League, Pee-Wee football or some other youth sport.

WSJ: Ref's death a consequence of lack of sportsmanship