The Security had to try and apprehend the thief by shepherding her around like a sheep until the police arrived without touching this disgusting thief. The fear of hurting the thief and the thief putting a claim in for compensation appeared to far outweigh the need to stop this thief and protect the customers. This world is becoming obsessed with making life so bloody daft. - If I see a thief stealing ill try and bloody stop them - if i see anyone hurting anyone for no reason ill try and stop them - ill not look away and think "better not get involved in-case they sue me!" So it appears that you are not safe from anyone or anything in a supermarket as the security can only act like Shepard's, so if someone steals your purse or wallet, best scream and hope the public stop the culprit and get running after the bastard yourself and if you get the time while trying to get your purse or wallet back try and call the police.
So lets say you have just fought a thief and knocked it to the ground - its hurt - you kick it like it deserves, chances are you will be put away behind bars and thief will be given a warning - this is how stupid the law works. So this is why the security forces in your local supermarket are pretty powerless to stop criminals, but the forces of human nature would hopefully come into play and surely no-one would allow an old lady to have her purse stolen right before their eyes if they were there - would they??? - I wouldn't allow it - would you??