Doubtless we'll never really know how or even if.
Here’s a story about some people who were poisoned with it:
It sounds like it’s relatively fast-acting. Which means he’d have been dosed 5-15mins before keeling-over on his front sidewalk. Only “slightly soluble in alcohols” probably means that there’d be a ‘scum’ on the win glass’ surface/sides, and traceable.
Wow; too many possibilities. It’s making my head spin.
Would it show up in a tox screen?