As a security guard he is a conscientious employee, but he feels that he isn't valued by his boss and you can see his frustration building as the story unfolds. As a consequence he plots an audacious robbery. Once he has decided on the heist he distances himself from his wife and his normal work partners so as to not implicate them. Then, with meticulous planning, and reliance on the very poor procedures at his security company, he literally just drives off with 11.6€ million, thus the title of the film.
These events took place in 2009, after the financial crash of 2008, and far from being regarded as a criminal he was actually admired by a lot of people - a Robin Hood sort of character - although his motives were nothing to do with being a robber of the rich to give to the poor.
He ultimately hands himself in to the police in Monaco. You get the feeling that the police officer who interviews him is also showing more admiration than disrespect for him, as he points out that as he has no arrest warrant, Musulin could just walk out.
I won't spoil the ending!