the thing is, if you had attacked the attackers and killed them, you would also find yourself up for murder, too.
This happened out of the blue, so bystanders cannot be blamed for not wading in - probably didnt understand what was going on until much after the event.
As far as 'wading in' is concerned, even the rozzers who shot the attackers have to follow what are termed 'rules of engagement'; meaning as they didnt witness the event themselves personally, it means they would not have been allowed to open fire.
If the attackers had surrendered, they would simply have been arrested for their crime.
The only reason the rozzers could shoot the *****, was they were attacking them - this permits firearms to be used.
By the way, the rozzers on discharging their weapons, will be subject to immediate arrest, themselves, until they can prove they were following rules of engagement fully. How bizarre is that?