To have a proper justice system.

As the main comment explained: this is not saying "you got the wrong result", this is saying " the way you reached that result is not the proper way for our justice system".

So they are just saying that the lower court didn't do it's due diligence and needs to look again at the case, this time considering the parts they missed the first time.

It is not uncommon in Germany that cases like this end in the same result

To try and explain it in an easier to understand way:

Person X murders Person Y

Court A says "Guilty, because you suck"

Court Higher B says: "Suckiness is not a proper judicial term, do the whole thing again"

Court A says "guilty, because here is the witness testimony, your finger prints on the murder weapon and the video footage of you killing person Y".

Same result as before, but this time in a proper manner fitting a proper judicial system.