When a US news team received footage of a mysterious flying object from a local UFO spotter, they decided to send out a news crew to prove that it was just another hoax.
But after filming at the same spot in Denver, Colorado, they recorded similar footage - and not even an aviation expert could explain the sighting.
The Daily Mail explains that the original footage was sent in by a man who didn't want to be named. It shows a series of objects flying in and out of the clouds at great speed, which he captured using a digital camera from a hilltop in Federal Heights, downtown Denver.
He said that the objects appeared between midday and 1pm at least two or three times per week and fly so fast that they are barely visible to the naked eye. However, slowing down the film allows them to be seen quite clearly.
News channel KDVR enlisted the help of former pilot, instructor and FAA accident prevention advisor Steve Cowell.
He explained that he knows of no aircraft that flies so fast and said: "It is very strange."
He could only offer one possible explanation, saying: "Perhaps there is some sort of debris that is being raised up by some of the atmospheric winds."
The Federal Aviation Administration told the news channel that air traffic control had received no reports of the activity described.
Click on the image below to watch footage of the Denver UFOs...
Is it a UFO or just a cloud?
UFO-shaped object found at the bottom of the Baltic Sea