Mr Day's friends, Marc Smart and Steve Kimberley, both 21, who studied with him at the University of Essex, are helping police piece together the events leading up to the incident.
A source said: "We're not clear yet whether he slipped because he lost his balance as he ran with just his socks on or whether he was running too fast and couldn't stop in time.
"But he crashed through the window and fell more than 40 feet from the corridor which was on the fifth-floor.
"We believe the victim had been drinking and that may also have impaired his judgement."
The hotel refused to make an official comment but a receptionist said: "The dead man was with two friends who are talking to the police at the moment. We don't expect them to return to the hotel."