Gagan decided to make a new upgraded pod however, these new pods would be twice as likely to cause problems. The sleep pods concentrated the build up of sleep dust in the users eye(which is made of cells) these cells evolved into organisms called Sandmen. While testing these pods. Gagan and his crew were converted into sandmen. After Gagan was in there, the dust preserved his human form and controlled him.
Rassmussen plotted to spread the encoded signal the Morpheus pods used to create Sandmen across the solar system. In doing so, he orchestrated a scenario filled with plot twists and a climax on board for dramatic effect "like a story", and send a video of this story with the signal.
In this staged story, Le Verrier went silent, and a rescue team from Triton, as well as the Twelfth Doctor and Clara Oswald, arrived. They went looking for Rassmussen, and he appeared to be killed by a Sandman. After being found again, Rassmussen claimed the Sandmen had made it very clear to him that they were "the future" and "a better life form", that they spoke to him in his mind, and he lied that they had spared him. He lied and pretended that his plan was to spread the infection of the sandmen via transporting one of the sandmen across the galaxy. He appeared to die again when Nagata, the commander of the rescue team, shot him. At the end of Rassmussen's video when Le Verrier's gravity shields were destroyed he revealed his plan, the recording blips in the video were part of the morpheus process that changes the chemical elements of the brain. Which would cause anyone to watch it to turn to dust by the end. He turned into dust and in the process revealed he was a sandman all along. (TV: Sleep No More)
The footage that Rassmussen recorded was later used in the episode of Doctor Who entitled Sleep No More, which was broadcast in late 2015, and was availible on BBC iPlayer by 2020. (WC: The Zygon Isolation)
Behind the scenes
Rassmussen is one of the Sandman enemies in the Doctor Who: Legacy mobile game.