I would not put chemical warfare or bioweapons past Putin. In fact, it's perfectly in line with his previous usage of nerve agents to assassinate his political opponents. However, I recall the U.S. vehemently denying funding gain of function research in Wuhan where it turns out they actually did fund experiments with bat coronaviruses. So likewise, I would not put it past the U.S. to have been funding whatever twisted experiments in Ukraine just as they were doing in China. I have yet to see any evidence of this, of course, but it's not a wild theory. It took something like a year before the NIH admitted what was going on in Wuhan.