Let's face the facts, some baggage handlers at Heathrow were caught a while ago pillaging luggage on CCTV during a police operation, so it does happen. I don't recall whether it was a BA or non BA baggage operation.
However, in 28 years of travelling heavily, I have never suffered a theft from checked baggage.
Last year I did have a bag forcibly opened and written off, when it was wrongly delivered to a carousel at Mulhouse aiport, instead of transiting through Basel to Palma.
No doubt that was someone's (FR or UK) customs forces having a look, since none of the contents were taken.
So I agree with the earlier that it is very unfair to label baggage handlers as thieves, but equally I do sympathise with the FA whose loss Chandler's Dad reports, since the data is there to show that some thieving happens.
Purely as an anecdotal aside, I read some time ago that white collar/executive crime is far more frequent than people realise, because it is kept low profile.