The murderer has fled the scene, you have a feeling he will try to leave the country. You get access to his credit card records and see that he has recently spent £500 on flights at Getaway Travel Agency. You immediately rush to the shop to inspect their records.
Unfortunately, Getaway is a very old-fashioned Travel Agency and they still use hand-written tickets with carbon-copies. Even worse, the staff have no memory of the man who bought the ticket and the carbon copy has not worked very well.
All you can see for the departure airport is:
"The what?" you ask the manager.
"I don't know," says the manager, looking puzzled. "We always write-in the full name of the Departure airport in that box".
Being the genius that you are, you immediately dispatch your men to the correct airport where he is arrested boarding the plane.