The police reported to the scene, investigated, obtained the hotel's record of its issuance of key cards for your room, investigated the hotel's log of who had used key cards to enter your room and at what time, and concluded what? If this was an employee, there would be a log of the creation of an additional key card for your room, or there would be a record of an employee entering with a master keycard such as the ones that cleaners use.
Have you been in touch with the parent company about the burglary and the indifference of the front desk staff?
Were you able to suggest to the police anything that might have attracted a thief's attention to you? If this is an inside job, but with no prior or subsequent room burglaries, it would be a huge risk without some expectation of a really big payoff. Did you ask the police about other incidents at the hotel or look for media reports of other burglaries? You say that all of your stuff was packed - do you mean that the thief took your packed luggage?

