This was a coordinated group of people who procured body armor, radios, and firearms, and planned to break into a Federal facility. Responsibility for this incident doesn't rest exclusively on the hands of the shooter.
An analogy is Enrique Tarrio's arrest in the wake of January 6th. Right wingers complained that he wasn't even in the capital during the riot. But of course that's not evidence his innocence. Even though he didn't personally participate in the putsch, he was still held responsible for organizing it (not for long on account of his pardon, unfortunately, but he was still rightfully convicted).
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.
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.
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.
An analogy is Enrique Tarrio's arrest in the wake of January 6th. Right wingers complained that he wasn't even in the capital during the riot. But of course that's not evidence his innocence. Even though he didn't personally participate in the putsch, he was still held responsible for organizing it (not for long on account of his pardon, unfortunately, but he was still rightfully convicted).