On the other hand, an apartment where someone killed someone else, or suffered a psychotic break and had to be institutionalized permanently, or died of mysterious causes? Higher-than-average likelihood of mold, lead, mercury, carbon monoxide, etc.

I'd probably do an extra review of environmental factors to be safe (as I would with any below-market apartment), but it's unlikely that even the majority of deaths are driven by persistent factors.

Me too with open arms.

A superstitious person's plight is another person's delight.