Airline responsibility for checked in luggage

Can anyone advise me on the airlines responsibility for checked in luggage left in there care, the lock on my mums suitcase was cut off and her suitcase had been opened and tempered with, during a recent flight from OR Tambo International to Port Elizabeth. Do the staff have any responsibility for the safe storage for items in there care?

We fly Mango very often and I am highly disappointed with this. Why should I use Mango airlines going forward.