I didn't say I was either, but again, what you're saying is just conjecture. The examples you gave on that ropey website are all examples of crimes committed by people who we did have record of and didn't get away with the crimes, so they're irrelevant to your wider point.
If you can provide some evidence that demonstrates that unsolved serious crimes were more often believed to be committed by unknown illegal migrants than not, then you might have a point, but you haven't so you don't.