So, some thoughts around the Bloody Sunday situation:
In general, I think that "we don't respond to social/political problems by cheering on the repressive arm of the state" is a solid and important principle, whether we're talking about knife crime or fascist organising or whatever. But I struggle to see how it can be applied to situations like Bloody Sunday (or Orgreave, Hillsborough, spycops, blacklisting, Grenfell, etc).
There's still the more pragmatic argument to be made that it all shows that going through the state is a very ineffective way to achieve anything that could be called justice, that you might or might not get charges brought against one scapegoat nearly fifty years down the line, but to say that the CPS/PPSNI have done a very ineffective job very slowly with regards to Bloody Sunday is still to implicitly say that the prosecution should have acted faster and more effectively, which... is that what I, or we, want to say?
Also, because these situations tend to be ones where the official record has been very distorted, there's usually also just a demand to get the true story out there, which I guess is a lot more straightforward and easy to endorse, but just getting the record corrected isn't the same thing as "justice", whatever that is. So yeah, what attitude do/should anarchists and libertarians take, or what role can we play, in justice campaigns in this scenario? Are there any solutions we can propose that aren't based on carceral logic, and if so what do those look like? Especially in these cases where so much time has passed - "troops out of NI" would be a reasonable anti-statist response in 1972 just like "cops out of the mining areas" would've been in 1984, but they're both a bit weak in 2019.