The pilot of the plane notified air traffic control of the threat, which was found on a note in the rear galley of the plane by a flight attendant.
"Flight 1500 now declaring an emergency at this time. We have a written threat aboard the aircraft," the pilot said. "Our flight attendant found a note indicating there was a bomb onboard towards the rear of the aircraft."
The plane, which was en route to Denver from Detroit, arrived safely at Denver International Airport and was taken to a remote location at the airport for screening.
"The FBI came on board the plane and asked, of course, did anybody leave the note. They said there was a piece of paper in the back with the word bomb written on it," said passenger Joe Vance.
One passenger, Tone Sevy tweeted information about the search and photos as he awaited heading back to the terminal.
K9 on plane, buses, checking us & personal bags. Sprayed with water before we deplaned. @Delta And TSA on it. Crazy situation— Tone Sevy (@ToneSevy) April 18, 2014