Shell Casings Allegedly Used in 'Brazen, Targeted Attack' of UnitedHealthcare CEO Had Words Written on Them, According to Authorities Brian Thompson was fatally shot outside a hotel in Manhattan.

Brian Thompson, 50, the CEO of UnitedHealthcare was fatally shot Wednesday morning in Midtown Manhattan.

Thompson was arriving at the Hilton hotel around 6:46 a.m. for UnitedHealth Group's Investor Day, which was being held in the ballroom, where a masked man waiting for him.

"It appears the suspect was lying in wait for several minutes and as the victim was walking to the conference hotel, the suspect approached from behind and fired several rounds, striking the victim at least once in the back and at least once in the right calf," NYPD Commissioner Jessica Tisch said in a Wednesday statement.

Thompson was taken to a local hospital before being pronounced dead.

Police sources told ABC News late Wednesday that shell casings found near the scene had the words, "deny," "defend," and "depose" written on them. Authorities did not elaborate, though several posts on social media suggest it could be in reference to the 2010 book, "Delay Deny Defend: Why Insurance Companies Don't Pay Claims and What You Can Do About It."

Thompson's wife, Paulette Thompson, said she's "shattered" by the "senseless killing" in a statement.

"Brian was an incredibly loving, generous, talented man who truly lived life to the fullest and touched so many lives," she said. "Most importantly, Brian was an incredibly loving father to our two sons and will be greatly missed."

UnitedHealth Group canceled the Investor Day event.

"I'm afraid that we – some of you may know we're dealing with very serious medical situation with one of our team members," UnitedHealth Group staff said during the investor day, according to a transcript, per CNBC. "And as a result, I'm afraid we're going to have to bring to a close the event today, which I'm sure you'll understand."

UnitedHealth Group, which is UnitedHealthcare's parent company, is No. 5 in the Fortune 500. Thompson was named CEO in April 2021.

NYPD Chief of Detectives Joseph Kenny at the press conference that the shooter ignored other people in the area.

"The shooter steps onto the sidewalk from behind the car, he ignores numerous other pedestrians, approaches the victim from behind, and shoots him in the back," Kenny said. "The shooter then walks toward the victim and continues to shoot."

"From watching the video, it does seem like he is proficient in the use of firearms," Kenny added.

The investigation is ongoing and no arrests have been made, per the NYPD.

"We will not [rest] until we identify and apprehend the shooter in this case," Tisch said.

This is a breaking news story and will be updated.