Every day there are thousands of crimes committed in America, and there are many suggestions for preventing them, but in the case of crimes committed by people who are here illegally, every single one of them could have been prevented if that person had been blocked from coming or been returned to his native land when he did arrive here.
Sure, the native-born population includes plenty of creeps, criminals, thugs, and bad guys, and they commit many crimes - and the same solution applies to them, except that instead of being deported as illegal aliens, they could have been incarcerated as career criminals. Multiple felonies are committed by folks who have a record "as long as their arm," and if they had been serving time for their crime instead of being free on bail, on their own recognizance, awaiting trial, or after serving a minimal sentence, the thousands of violent crimes this group of people commits would never have happened, either.