"Magnus Nordenmark" is the name used by the tabloids. https://www.findagrave.com/memorial/250492078/sven-magnus-no... has the right date of death, and gives a grave site of plot SO 33 5756 in Solna Cemetery, Stockholm. (I don't know how to verify this without actually visiting the cemetery.)
My google fu aint what it used to be, and when I google 'Sven Magnus Nordenmark' my own comment right above this one is the top hit.
With the death date I was able to find https://sv.metapedia.org/wiki/Jacques_Wallner and its references including http://web.archive.org/web/20140428113854/http://www.natione... which is a detailed review of the whole affair. These are far right / nationalist sources but I don't see that as a reason to disbelieve them, the whole thing sounds a lot more plausible if you are one to believe that a court would let a guy off on self defense if the eyewitnesses painted the victim as a nazi who picked a fight.
If it's misinformation I guess I'm participating in resurfacing these sources on a highly indexed website, but I don't mind being able to add context to somebody's accusation of murder. Nothing catches my interest more than a good wiki edit war.
The account in the Nationell Idag article does (eventually) provide a few cross-referenceable claims.
> Vad som däremot är märkligt är hur händelsen beskrevs i en av våra största kvällstidningar, nämligen Aftonbladet. Rubriken dagen efter löd 'Jag är fascist' – då höggs han ner.
Allowing for some hyperbole, we're looking for Aftonbladet headlines on (or shortly after) 1982-03-19. I'm again suspicious that the author made a more concrete reference to an article that doesn't support the claims, but superficially appears to:
> En av många artiklar om våldsamma skinheads som publicerades under denna tid (Aftonbladet, 20 juni 1982).
But they recover some of my respect by finally providing concrete court dates:
> Den 11 juni, efter knappt tre månaders utredning, föll domen i tingsrätten.
> Hovrätten dömde Jacques Wallner till 18 månaders fängelse den 17 december 1982.
These dates might help relocate the court documents (which were online, but have since linkrotted). Lots of things claimed at the beginning of this article that seem as though they would be "facts of the case" (e.g. statements about what testimony was given) are later described as the claims of an unnamed family member of Magnus.
You could have looked this up yourself.