For a crime older than I am, was there even any justice served at this point? The man wasn't actively a threat to society and was instead used as an experiment subject.

Amen. In my view, punishing people for crime is never about justice and always about sadism. Justice is social. Social justice. We should get at the systemic root causes of why crimes are committed in the first place and reduce the rate at which they are committed by addressing those systemic causes. But the false "justice" of the sadistic vigilantes and the reactionaries is to leave the root causes of crime unaddressed, so that they have a never ending supply of convenient scapegoats. Why put an end to things like poverty and addiction when those things are profitable? Why reduce the supply of criminals when you can make a lucrative career out of "defeating crime" by sadistically capturing and punishing individual criminals? These people don't want crime to go away, they want to broaden the definition of crime so that they can capture, enslave, and execute as many as possible.

The only cases I'm even sympathetic to execution are of the monsters that lead to hundreds of deaths through social murder or negligence

Those are precisely the cases which go unpunished because they are crucial to the reproduction of the system as it currently exists. But even this can be addressed systemtically: By getting rid of a system which rewards sadistic vigilantes (cops, judges, prosecutors) with power and prestige.

I would add all C tier executives and board members (and shareholders that hold enough to be just below the board) in any and every company that is large enough to be multi-state/national. Especially those that create the "too big to fail" situations like banks and investment funds. Also including of course the entities that treat basic human needs like housing as stocks to be made more and more costly. So would mean landlords, HOAs (especially those that are not even actively living in the area covered), and fuck it, just no trial required for the insurance (medical and other) and pharmaceutical companies. Along with the politicians taking any money/stocks/kick-backs from any of the groups mentioned (though I am also fine with just literally all current and previous leaders of both false parties).