In fact the take-off from the taxiway was NOT cleared by the controller. The pilot was cleared for a normal take-off from the runway, and read back the clearance correctly. He took the taxiway for the runway by his own mistake. The controller did not realize the pilots mistake in time to avoid it. That is the only mistake he can be blamed for.
The airport is equipped with ground surveillance radar using Mode S, but I have no information about the serviceability of the equipment at the time if the incident.
The interesting point is, that DFS is not taking action because of the incident, and is not asking whether the presence of two or three people in the tower would have helped to avoid it, but is only taking disciplinary action because of falsification of documents. And therefore I think, removing some 30 year old-controller completely from duty is a bit hard. The other two are 40 and 44 year old. They loose parts of their income (1,5 Million Euro for the 30-year old, calucualted to end of controllers career), parts of their company pension, maybe their houses or whatever. Still think this is fair for people who did a good job for years, and now are caught for falsification of documents?