I very much do not believe that we should be forced by law to intervene in any way.
You have to be careful with all this 'there ought to be a law' crap. It goes too far, people overreact.
Every bad decision cannot be made illegal in order for it to never happen again, nor should it be.

There is another 'law' that these people should be subject to and that is morality. Society will punish these people if it feels that what they have done is wrong, or at least, it should be.
The power of society's ruling can be much stronger in affecting people's decisions and morals than being held responsible by a legal system.
And this is as it should be.
An event like this strengthens our morality.
People come together on forum to discuss the topic, to pass judgment and berate the guilty.

As far as answering the question above, I do not believe I have enough information from this article to decide that.
If the attacker had a gun and you risk being shot, would all the cowboys in the room still run 100 feet towards the attacker giving him ample chance to shoot you?
Maybe that's another question. How far does your personal moral duty extend?