The indictment doesn't allege that the defendant sold it, only that he wrote it and someone else sold it.
And as you know, white hats create proof of concept code all the time. And give it to various people (including, in the end, anyone) for various meritorious reasons.
Watch the video of this horrendous deadly baseball bat attack. Baseball players do not bludgeon people to death with bats all the time. Therefore, baseball players should never worry that they might be falsely accused of an attack. Oh, and the crime was horrible, so that means the evidence must be pretty good. Q.E.D.
And as a malware researcher when he became aware that his proof of concept was indeed being used to conduct fraud, he turned a blind eye?
The least plausible part of this chain of events is that Kronos, from what I can see, is not a very interesting piece of software - more a tedious exercise in plumbing than an interesting proof-of-concept.
People on this thread have a lot of strange ideas about what infosec people do in their jobs.