So, there is a bunch of countries in Europe that made a promise to each other to help catch bad guys who run away. This promise is called the European Convention on Extradition.
Let's say a bad guy named Bob committed a crime in France but then ran away to Germany. France could ask Germany to send Bob back to France to face punishment for his crime.
But there are some conditions that have to be met. The crime Bob committed has to be considered a crime in both France and Germany, and it can't be a political or military crime.
Also, the evidence against Bob has to be strong enough to convince a judge in Germany that it's worth sending him back to France. And Bob can't be sent back to France if he is in danger of being persecuted or punished unfairly there.
It's like a big team effort to catch the bad guys and make sure they face justice for their actions, no matter where they try to hide.