A passenger died on a flight out of Denver although passengers performed CPR for nearly half an hour Sunday on a United Airlines flight en route to Salt Lake City.

Salt Lake City International Airport spokeswoman Barbara Gann confirmed the death of a passenger on United Flight 5596 on Monday.

A passenger on the flight, Jared Noall said 15-20 minutes before the plane landed, he noticed a passenger snoring loudly but then suddenly stopped however many passengers assumed that he just slipped into deep sleep. However once the flight landed, they realized something was wrong.

"You could tell something was wrong. I asked, 'Hey, sir, are you awake?' I shook him a bit, trying to see if I could get a response out of him. We checked his throat for a pulse, and it wasn't there, so we laid him down in the aisle and start CPR," Noall said.

The man who died on the flight has not been identified, airport spokeswoman declined to release the passenger's age, gender, or name. She said the airport police are conducting their investigation.