Allegedly Olof Palme's was also a political assassination.

Probably, but that's never been resolved.

Now, how do you suggest Europe can prevent political assassinations from happening other than instituting some sort of thought police?

I have never said I believe it can be prevented outright. That would be pretty daft.

I have said that yielding to threats is not going to help. Rather it will encourage those making such threats.

Keeping known extremist factions under surveillance, as is being done all over Europe, is obviously also wise.
 

The world's northernmost desert wind.