Innocent 20 year olds who feel like they might be charged with murder would do a lot of things I would say, including pointing the finger at someone else and changing their stories, and denying that someone was with them. 

All of these actions can be explained by fear, naiveity, the trauma & shock of finding your roomate dead, youth and the pressure of interrogation in a foreign country where you don't speak the language fluentely.  They don't equal murder.

People do stupid things when faced with the idea of jail, even if they haven't done the crime.