UnitedHealth Group's investor day turned from an ordinary corporate meeting in a midtown Manhattan hotel to a scene of stunned grief quicker than the health insurer could even react.

"It was mid-presentation when everyone began to get the headlines,” said Michael Ha, a health-care analyst at Baird who sat among roughly 275 attendees at the Wednesday event when news alerts started pinging attendees’ mobile phones. "We were all looking around; we were all shocked and confused."

Fifty-year-old Brian Thompson, who led the company’s UnitedHealthcare insurance division, had been fatally shot on the sidewalk as he approached the hotel around 6:45 a.m. Blood stained the concrete. And the suspect was still at large.