Private guards eh?
They were of course "allowed to interfere", you could even go as far as expect it from them; there is no rule or conduct that forbade that. They just
chose not to.
Privatizing profits is good for you. Socialising losses is even better.
edit: some uniform-wearing person told the journalists that they were not allowed to use force because "human life counts more than jewels".
The curator also said that guards were not allowed to use physical force.
Another source claims the guards carried machine guns. Another source denies it.
