Comvined with the fact that most EU countries have much lower crime rate than US and have no death penalty, it shoupd be clear that death penalty is totally ineffective at reducing crime. There is literally no place on earth where you can demonstrate "we introduced death penalty and crime has fallen" by any significant amount. We do, however, have ironclad proof that rehabilitation makes a difference. We have proof that quality of investigators that make sure the perpetrator is caught for sure makes a difference.
Recently in UK our inconpetent government has reduced the amount of police resources avaliable to investigate crime. More crimes are unsolved, crime rates increase because criminals are unounished, and they are hoping to compensate with tougher sentences. And that iduotic because we know it doesnt work, it never did