failing to protect its citizens, surely?

This asylum-seeker chap was known to have links with extremists, under investigation for preparing a violent attack against the state, was on a US no-fly list, and was known to have been in contact with ISIS.

Clearly there wasn't enough evidence to convict him of a crime in Germany, but surely there was enough to declare him a danger to the German public and place him on a flight back to Tunis?