Unless the computer shop (employee) installed malware that can be traced back to them (for instance a key logger that emails the Bitcoin Core password to someone), it will be virtually impossible to prove they did it. Without evidence, OP could just as well have moved his own coins, or someone else could have gained access to his computer.
Maybe a sudden lifestyle change of one of the computer shop's employees can be used as circumstantial evidence.
Or, unless the employee made a habit out of robbing clients... One case means nothing, but if a couple dozen people claim to have been robbed by the same store in the same timeframe, it might force law enforcement to take a closer look....
For all the OP knows, maybe the shop owner already caught an employee stealing from other clients and terminated him, or reported him to the police (theft happened almost a year ago, so if there were other cases, odds are they already came foreward to either the police or the shop owner). Maybe he goes to the shop and the shop owner immediately tells him which police department is handling the case... Stealing employees are not good for a shop's reputation, so (unless it's a one-man shop, or the thief is the owner) odds are that once the owner had several complaints, he himself would have dealt with the stealing employee.
Ofcourse, these are a lot of 'ifs and buts', but still, it's worth filing a police report and going to the shop to ask them if they know anything about this (without accusing them directly, i'd personally take a lawyer with me if i was planning on making big accusations).