As German news sources repeat over and over, the German FBI, the Bundeskriminalamt (BKA), has insisted that migrants are no more violent than "comparable" Germans, although there is never any detailed information about what the BKA considers "comparable" in the news reports. In any event the BKA report for the beginning of 2016 recorded 69,000 (g) attempted and completed crimes by foreigners, mostly theft and fraud.
Is this a problem? It depends on your perspective. If you think Germany has an obligation to offer a new life to millions of randomly-selected people from around the world, then you'll argue that some extra crime is to be expected, and we'd do best simply to ignore it.
The other perspective would be that Germany should proactively screen out as many criminals as possible. This is nowhere near as hard as people make it out to be. We have lots of information about what predisposes someone to crime. Past criminal history, low IQ, low impulse control, low levels of education, status of being a young male. Everyone who seeks to enter Germany without an existing job offer or university acceptance should have to provide detailed information and complete a series of tests.
Immigration into another foreign country is not a human right, except for refugees (and even refugees have a right only to locate to the first country in which they are no longer persecuted. The rest is migration). Countries are free to place whatever restrictions they choose on who gets to enter their country.
Germany is more stable, prosperous, safe, orderly, and humane than 95% of nations on earth. This leads to two conclusions. First, Germany has a lot of leverage, because tens of millions of people want to come live here. Second, Germany has a lot to lose, because letting in (1) large numbers of (2) the wrong kind of people could damage Germany's stability. As the German Social Democratic jurist Ernst-Wolfgang Böckenförde once said (pdf), "The liberal, secularized state is nourished by presuppositions that it cannot itself guarantee." Import enough people who don't share those presuppositions and you import social conflict.
This is why I say the ideal crime rate among immigrants is 0%. That is, Germany should aim to import people who are less likely to commit violent crimes than "organic Germans", to use the phrase which has popped up in Germany lately (bio-Deutsche). We'll never get to 0%, of course, but that should be the goal. We can certainly eliminate 80% of violent crime by migrants by not allowing in any uneducated, low-IQ young males.
The right analogy, in my view, is nuts and rocks. Here's my argument. When you harvest nuts, a certain number of small nut-shaped rocks enter the hoppers. If you bite down on a rock thinking it's a cashew, you may well lose a tooth, or more. In fact, this is one of the main sources of business for personal-injury lawyers. These days, food companies have gotten very, very good at removing rocks from nuts before they reach the consumer.
Why? Because society has determined, by regulation and lawsuit, that the ideal number of rocks in nuts is 0%. Society decided 1 rock in 1,000 nuts is too much. In fact, 1 in a million is too much. Because if you're the person who bites into that 1 rock among a million nuts, you have suffered a serious, preventable, totally unnecessary injury. Nobody -- not even food packaging companies -- will argue that even 1 rock in a million nuts is an acceptable risk. Because it isn't.
This is the analogy we should use for migrant crime. Germany doesn't have to let any migrants into its borders, except those recognized refugees who flee directly to Germany without transiting a country in which they would be safe. Immigration is a voluntary choice by the receiving country. Allowing immigration is, in theological terms, supererogatory.
Therefore, any serious crime committed by an immigrant is analogous to a rock among the nuts. It didn't have to happen. It could have been prevented. It's not simply an inevitable fact of life we must all accept. Crime by your fellow-countrymen is. This is why no country allows you to sue the police or the government for personal damages simply for not preventing a crime which happened to you. Not even if they had advance warning you were at risk. If the rule were otherwise, the courts would drown in litigation.
But I think the policy should be different for crime committed by immigrants. These crimes, unlike crimes committed by natives, are not simply part of the background radiation of risk we face. They happened in Germany, to you, only because the German government failed to responsibly screen immigrants. The German government let in a rock among the nuts. And trust me, it's letting in far more than 1 in a million.
We should strike to ensure the number of rocks among nuts in our supermarkets is 0.
We should also strive to make sure the number of serious violent criminals among immigrants to our country is 0.
We'll never get all the way there, but the goal should be clear: 0.