The "smoking gun" here is, I suppose, that the person in question was fired from _another_ project in quite a public fashion for engaging in the very same sort

The "smoking gun" here is, I suppose, that the person in question was fired from _another_ project in quite a public fashion for engaging in the very same sort of harassment the OP reported to his supervisors and was rebuffed for. There really doesn't look like there's much wiggle room here. Now, that said, I think this is brilliant because this sort of thing happens _all the time_ -- typically, if you report a Higher Value Person(tm) for harassment (no matter what the field) you may as well just be shouting in the wind. You'll get told "oh, you don't want to ruin their life, do you?" or "I've spoken to him, he won't do it again, please won't you take one for the team?" And if you persist, well, you're just disgruntled and unhappy and maybe you should go somewhere else. Nice to see someone held to account for once!