Usually when items are stolen from a checked bag, they're valuables, often jewlrey, electronics, or medication with a street value. Common sense dictates you should never pack such valuables in checked luggage, but people do.

The problem with locking luggage is the checked luggage screening devices and procedures used in the US. The CTX machines generate alarms from common items people pack and the bag then has to be opened to resolve the alarm. At other airports without CTX, a percentage of bags are opened for ETD swabs on the inside. While I support the screening of checked luggage, the system in the US is inefficient and primarily relies on CTX technology which causes many alarms. It is my understanding when purchasing the CTX, much of the decision was political as there are other, less intrusive methods of screening checked luggage.

As far as items being inserted into suitcases, I have read about other documented cases in the past. I've read reports of passenger luggage being used to transport large amounts of cash from the USA to Central / South America. Whether it's drugs, cash, or other items, it's important to lock luggage to prevent the introduction of items.

Last but not least, it's also wise to lock luggage to prevent your luggage from accidently being opened while in airline posession. Zippers sometimes get caught on belts and when someone goes to pick it up, the items fall out.

Airlines around the world, except in the USA, advise you to lock your luggage for good reason. Heck, the TSA at Newark even managed to plant a "fake bomb" in someones unsecured suitcase which was supposed to be caught in a screening test, instead it arrived in Amsterdam.

SDF_Traveler