If you feel that your proof of a Nrcprm2026's involvement is iron-clad, a place to go might be the arbitration enforcement board. Fill out the form given, link to the arbitration action being broken (in this case, the indefinite ban for socking given at the bottom of WP:Requests for arbitration/Depleted uranium#Log of blocks and bans), present what evidence you can, explain that you have additional evidence that involves quoting that editor's real name (and whatever else it was you searched on) and that you want arbcom to say "yes, go ahead" before posting it (it's used in the proceedings, so they'll probably tell you to go ahead but check anyways), and then link to the SPIs (and probably this thread as well for completeness), explaining that the SPI has been sitting idle for quite a while, presumably due to complexity and backlog. They'll want to see a rationale for bringing it to AE rather than SPI (or requesting help at WP:AN); the rationale is that a) it relates to an arbcom case, and b) you aren't sure what to do about real-name information and were told that they were the people to ask. Maybe also ask them if starting a LTA entry for this editor is a good idea (they've been socking for many years now; the indef ban was applied after two shorter bans for that). 

 The other option is to take a break from it for a while, and only start up again once they start socking again. When chasing long-term offenders, there's always the risk of getting too tied up in it. The end result of that tends to be either burnout or crossing the line into wiki-stalking or other harrassing behaviour (that's part of what Hillman got in hot water for back in the day). We've lost enough good editors as it is, so use your best judgment and don't be afraid to take time away to do things that are actually fun as well.