Explanation:
The crime rate statistic shows the number of registered crimes divided by the number of registered residents in a country or area.
“Registered” is important here!
If you add undocumented immigrants to the calculation, the statistic is skewed:
Undocumented immigrants aren’t registered as residents for the statistic, since they are, well, undocumented.
However, any crime committed by any one of them will count towards the crime rate when they’re registered by the police.
So even if they were much less likely to commit crime than the resident population on average, the crime rate statistic would still increase. The denominator of the equation doesn’t increase by definition, because only legal residents are counted towards the statistic. But the real number of people inside the country who may commit crimes increases.
This is important to know as context when people try to “prove” immigrants are more criminal than citizens, using the crime rate statistic.
Um Ackshually, there are many places where even “undocumented” people can be considered “registered” in this sense. “Undocumented” simply means lacking the authorization to be (and work) in the country, and is really just a minor paperwork violation unless an actual crime is committed in rhe process.
So, many localities will try and integrate these people into the community, and provide them the same local services everyone else gets, by simply not asking them to show their passport first. So, they might be able to get their name on utility bills, and use that as proof of residency to get a drivers’ license, in spite of their lack of status. (This notion that undocumented people still deserve human dignity really irks Conservatives, even though they all had ancestors who held the same status here at some point.)
This is really at the heart of what a “sanctuary city” policy is all about. It’s a recognition that a local government has a responsibility to all people living in it, regardless of their immigration status. And that local officials really don’t have the tools to be able to determine that anyway, so a local official won’t care about someone’s immigration status unless they are on the wrong side if the law. (Which also exposes the lie that these cities are less safe. If anything, sanctuary policies make it easier to kick out the miscreants, because no one is spending time chasing down undocumented people who are not causing trouble, leaving more time to find the bad eggs)