Gary Zalevsky, 47, of Sunny Island Beach, Florida, was dining with five associates when he suddenly jumped to his feet and unloaded up to eight bullets into Brian Weiss, 31, of Davey, Florida.
Zalevsky shot Weiss in the head, killing him, before taking his own life, according to cops.
The group was eating in a private room next to the main lobby of the hotel.
Weiss was the CEO of FWM Laboratories, a Florida-based food supplement company that was one of 50 firms sued in Manhattan Federal Court in 2009 for misleading consumers into thinking that Oprah Winfrey and another celebrity endorsed their products.
At the scene, at least one witness was put in handcuffs and taken in for questioning, but was not charged in relation to the shooting.