[thunderfork]

Responsibility is a separate question from correctly reporting on the events that occurred. "A protestor shot someone" is correct, "a protestor shot someone and the group is culpable" could be argued, but "the protestors shot someone" is simply untrue.

[Manuel_D]

No, it's entirely viable to say a group of people did something. E.g. "a lynch mob killed ______." Sure only one member of the mob actually tied the noose, but the mob as a collective took that action.

[thunderfork]

"one can say a group took an action in some cases, so it must be right to say a group took an action in this case" is not compelling.

[Manuel_D]

The point is they're both cases where a group of people get together to carry out a criminal act of violence. The fact that only one individual actually fired the gun or tied the noose doesn't alter the fact that the group as a whole carried out the criminal plan.