I wonder, in the case of mass violence events that were used as advertisement for the (assumed) murderer’s POV, whether there should be an equivalent of a House of Lords for the exceptional situation of censoring what in any other context would be breaking news. You don’t want or need (or be able) to censor a manifesto for all time, but you would want to prevent the (assumed) murderers from gaining any momentum from their heinous acts. So a ninety day (but only 90 day) embargo on public speech from bad actors, with the teeth of governmental enforcement, sounds pretty reasonable to me. Even cleverer to salt the ether with “leaks” that would actively suppress any political momentum for the (presumed) murderers during the embargo period, but with the true light of day shining after three months.

It doesn't sound reasonable to me tbh. If anything, reading those manifestos is a good way to learn just how nutty those people are in the first place. At the same time, having it accessible prevents speculation about motives, which can lead to false justification for politically oppressive measures.

OTOH if the goal is to prevent copycats then I don't see the point of a 90-day embargo. People who are likely to take that kind of content seriously enough to emulate are still going to do so. Tarrant, for example, specifically referenced Anders Breivik.