Swedish servers raided, no bits harmed

Swedish police have raided servers belonging to the ISP Bahnhof Internet. They discovered 23 Terabytes of infringing content. Apparently, one of the servers in the ISP was the largest file serving machine in Europe!

This case highlights an interesting question about ISP liability. Apparently, two employees are now suspected of being responsible. Assuming that the company didn't know about the misuse of the servers and the employees are found responsible, would this be enough to limit their liability? In most legal systems, employers have certain responsibility for the actions of their employees (responsibility in eligendo). The thing is, how can a company keep track of what the system administrators are doing? Who keeps the keepers?