(CNN) -- The FBI questioned passengers from a Delta Airlines flight from Detroit to Denver on Friday after a potential security threat.
"The majority of the Delta Flight 1500 passengers have been allowed to claim their luggage and continue with their travel plans," FBI spokesman Dave S. Joly said.
The screening that included police officers with the K9 unit delayed their arrival at the terminal by about four hours.
"Why did it take so long? What was the real holdup here? What were they really looking for?" asked Jace Booher, according to CNN affiliate KDVR.
A law enforcement official told CNN that a bomb threat found written on a note prompted the security screening after the plane landed at Denver International Airport.
The 737 aircraft, which was carrying 151 passengers and six crew members, landed safely at 4:40 p.m. MT as scheduled, said Russell Cason, a spokesman for Delta.
The plane was taken to a remote location at the airport for the screening.