(I've gathered the information from a couple of Dutch blogs, here and here, which in turn rely on Dutch news sources).
Readers of my vintage or older may remember the Red Army Faction, a violent leftist organization active in Germany in the 1970s and 1980s. They also did some business here in the Netherlands. During the "German Autumn" of 1977, when RAF activity caused a national crisis in West Germany, RAF member Knut Folkerts shot and killed a Dutch policeman. A Dutch court sentenced him to 20 years' imprisonment, but the government extradited him to Germany for trial on other charges there (he'd killed in Germany as well). He was convicted and sentenced to life in prison.
Eighteen years later, the German government released him. The Dutch government has been trying to get its hands on Folkerts so that he can serve his Dutch sentence here. Meanwhile, he's started proceedings in Dutch court to get his sentence quashed, I think (though I'm really unclear on this) on the basis that he's already done his time in German prison.
I gather that the German government hasn't been very cooperative with Dutch efforts to take Folkerts into custody. There is some hope that the new Merkel government might be more receptive, since the new interior minister is himself a victim of the RAF, which put him in a wheelchair. Earlier this month, the Dutch government again requested extradition of Folkerts. The German government has yet to respond.