I'd actually *expect* immigrants to have a higher rate of crime than the population in general. After all, you usually don't immigrate to a country if you were well off back home. Often you have just enough to get out and escape your circumstances and you're coming from what *I* would call a shit hole. But I'm a privileged 1st-world middle class white boy.
So, there you are in a new country with a different culture and likely less education. You tend to get a bottom-end job (jobs the natives don't want, which is why they tolerate immigration in the first place). If you're first-generation, you sound funny and the natives treat you like a second-class citizen. If you're the child of immigrants, you may still sound funny and you're still culturally odd.
Don't fit in, have trouble with the language, can't get a good job, possibly less educated, possibly from a culture that doesn't have the same standards for personal interactions. Probably some racism directed your way. Yeah, I can't see how that could translate to a higher crime rate!