Shooter had to have been a hired assassin/pro or someone with lots of tactical training/experience. He had a silencer. Fired multiple shots from about 20 ft away and did not miss. Came up on Thompson from behind so he had no chance to react. The shooter had an escape plan. Took an e-bike up to Central Park where he could quickly blend in with crowds going for their evening run/walk without being surrounded by cameras. Probably ditched his hoodie and mask and took the subway home.
Thompson was sued for insider trading after he dumped a bunch of stock after the DOJ started an investigation into whether United Healthcare committed antitrust violations. Thompson sold about $15 mil without disclosing to the public the information about the antitrust probe. But I doubt this had anything to do with it. Big execs regularly sell chunks of their stock as stock is the main way they are compensated. Since the lawsuit, United Healthcare's stock has done pretty well and was not affected much by the DOJ probe.
Immediately after the news broke, virtually everyone on twitter made the same joke that the NYPD was currently reviewing everyone who was ever covered by UHC as a possible suspect. But if someone was denied coverage and lost a family member or went broke, you would expect them to go for a full on shooting spree and go out with a manifesto in their pocket. This shooter had only one target.
Thompson doesn't seem like someone who would have been in trouble with the mob, Russians, drug dealers or the usual riff raff who would order a public hit. But who knows. Super rich people get into some weird sh#t.