https://smokinggun.org/police-suspect-used-bt-pistol-to-attack-unitedhealthcare-ceo/
No, the assassin didn't use a B&T Station Six. How do I know? Well, the gun is too freaking big. There's clearly smoke coming from the ejection port as the shots were being fired, that wouldn't happen with a Station Six because the reason why that gun is particularly quiet is that it isn't semi-automatic and requires the shooter to manually chamber each round - a large part of the boom boom comes from the ejection port (incidentally, this is also why is useless to try to suppress most revolvers - a lot of the boom boom happens between the gap between the cylinder and the barrel). Also, it's possible the the shooter was using subsonic rounds; but, 9mm usually travels faster than sound, and no suppressor is gonna make a sonic boom quieter. A subsonic round could contribute to the malfunctions that the murderer was dealing with.
What's more, the Station Six is a gun that's imported from Europe, costs over two grand, and is immediately regulated and registered under the NFA. It's pretty damn exotic in the states. If you're trying to murder somebody, and get away with it, you probably want something more common.
All that said, it's incredibly rare for suppressors to be used in crimes. All suppressor purchases require several hundred dollars in fees paid to the federal government. Again, all suppressor purchases fall under the NFA.
Suppressors generally don't make guns "whisper quiet." A suppressed AR is louder than a jackhammer. Suppressors are mostly used as a range tool to keep us from going deaf. Often, they're used on home defense weapons, again, to keep us from going deaf.
This is another case of the gun grabbers getting their gun information from Hollywood rather than living in reality.