Crossing state lines really does have certain jurisdiction / formal legal implications. In particular it upgrades the matter from state to the federal judicial system, which usually entails higher stakes for the defendant. If some group wants to see a particular individual punished for whatever reason, then naturally they would want him to have tripped over the technicality that would make his situation far worse. It has nothing to do with crossing the state line being a heinous act in itself.
I nailed everything from context except the particular crime being alluded to.