"As impressive as it is, it's still one tiny portion in the context of a vast amount of peripheral evidence" 
A US campaigner has vowed to release a video which he says proves the existence of aliens
Jeff Peckman, who claims the film features a living extraterrestrial, will show the footage to the media on Friday.
The 54-year-old is lobbying for a commission to be set up in Denver so the city can prepare for contact with alien life.
Mr Peckman promised to show the film to officials when he appeared before them earlier this month.
He told the Rocky Mountain News: "It shows an extraterrestrial's head popping up outside of a window at night, looking in the window, that's visible through an infrared camera."
Mr Peckman - who said the film convinced him that aliens exist and the city needed to act - said the creature is about 4ft tall and can be seen blinking.
"As impressive as it is, it's still one tiny portion in the context of a vast amount of peripheral evidence," he said.
"It's really the final visual confirmation of what you already know to be true having seen all the other evidence."
Mr Peckham added that other "related credible evidence" proving aliens exist will also be shown at at the news conference.
He said an instructor at the Colorado Film School in Denver has analysed the video "very carefully" and said it was authentic.
The general public will have to wait to see the footage as it is being included in a forthcoming documentary.
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