Judges, not juries or attorneys, determine what is legal. To be exact it is ultimately the nine judges of the Supreme Court.

Ultimately, yes.

Ultimately, you're correct, unless someone decides not to appeal somewhere along the way. Prosecutors will often take a jury's verdict as "the people have spoken" and leave it at that. Appeals are normally based on technicalities, not "we disagree with the jury, Judge, and we think you should tell them they were wrong."