Criminals should not be tried twice. There is a reason why double jeopardy exists. It makes sure that both sides are doing their best to win the case, because it can not be done more then once. It also will save the taxpayers money because they are not having to fund twice as many criminal cases.
Court cases are already taking too long for decisions. If we have to go through multiple trials and selecting a jury, it would be too costly and time consuming. Also, I could lead to a third trial if first find the innocent and second finds them guilt and the other way around. Furthermore, we have to appeal courts to go through cases twice.