society is already harmed by the initial crime, and now it has to pay the price a second time by forgetting?
strip the researchers' names and institutions from all copies of the articles, and adjust bibliographic standards of all reputable journals to require citations say the articles were authored by "Ethical disgrace" or whatever.
Here's a longish but well-argued explanation of why it's a terrible idea: https://www.jewishvirtuallibrary.org/the-ethics-of-using-med...
In any case, a retraction would not necessarily erase that knowledge. It would, however, limit its usefulness for the authors of these papers, in terms of reputation and citation count. That should serve as an incentive to more thoroughly investigate the provenance of that brain with a gun shot wound you're dissecting.
And no I dont view ill gotten evidence as a similar issue, seeing that the 'gained knowledge' is so narrow in it's scope.
Anyone can now replicate it.