If a murderer creates a file system/energy source/mouse trap that is effectively better than all of the alternatives, and generates value to the world, what he did in his personal life is effectively moot. There is no ethics problem involved in choosing the best solution to a problem, when that solution exists.
If financially supporting said murderer allows them to continue to possibly murder more, then I would say there is a moral dilemma. Less so when the murderer is in jail and unlikely to ever really benefit from your using said solution.
Which gladly rarely happens, so often you still have sufficient choice. Now, if it turns out Euler sabotaged some bridges and caused deaths, you'd still have a hard time avoiding using e.
But for software? It's usually rather easy to find alternatives. And ReiserFS never was an exception here.
The idea of “stochastic death” is a dangerous and unhelpful escalation of rhetoric that amounts to an excuse to call someone a murderer because they said something you disagree with. It’s the idea that Biden was somehow a “partial murderer” because he said something that might have, possibly, maybe, influenced a wacko to attempt an assassination on Trump. If we start calling everyone a type of murderer, it cheapens the word, dishonors the victims of actual murder, and hardens hearts with hate and fear of the dreaded Other when what the tribalists need most is a little mutual understanding.