In the same way that so called minor driving offences ( no tax, insurance, not wearing seat belts ) are often an indicator of the person being involved in other illegal activities ( drink driving , drugs , speeding ,car theft , burgulary etc) then a similar approach could be applied to immigrant crime. It is probable that the perpertrator ( if an illegal) has committed other crimes in his travels to get to this country. Getting into this country illegally is a crime isn't it? Once conditioned to commit a crime or two a few more probably won't worry him too much.