If somone wants to get into your suitcase they will. I have just had that experience. On my return from Bali I passed out on the flight and then was very sick. The poor purser with the sick bags. No-one was meeting me at that time of the morning so the ground staff insisted I went by ambulance to hospital. I was assured my luggage would be locked up and it would be delivered next morning when I was out of hospital.
It was delivered late that morning and I said to the courier all I was concerned about was whether my wooden items were still in one piece (you know how everything gets shoved back in the bag at customs. He said I was lucky that my luggage was OK and not damaged as some was.
To cut a long story short my luggage had been gone through (carryon and suitcase were still locked) and numerous things had been stolen.
It turned out to be the courier who had delivered my luggage. He was working for a contract company that delivered luggage.
At least my story has a happy ending as the Federal Police were waiting for him when he got back to the depot, they had had him under surveillance. Perth forumites would have seen this on the TV and in the newspapers. He is awaiting trial.
I collected my things this morning from the airport Federal Police. I was lucky as it seems he has been doing this for months. I am still amazed at how he got into the luggage. My suitcase had an extra strap around it but this had been worked loose, but still also locked. Obviously where there's a will there's a way, but not for anything good this time.