What is it called when everyone confesses their guilt / involvement in solidarity, but there is only one confessing truthfully?
Solution 1:
You could refer to it as "Spartacussing" or "Spartacizing", in reference to the famous scene from the movie Spartacus where an entire captured army shares the punishment for leading a rebellion rather than give up the true leader to suffer by himself. (A clip of this scene is available at youtube.com, and it is referenced as a well-known trope on TVTropes.com.)
I should point out that this is not an established word, but it is likely that a reasonable number of people will recognize the reference.