Why didn’t the judge order a new trial? if the witness is unreliable, isn’t that for a jury to decide? It seems like there wasn’t any proof he lied in this case.
It's not within the appeals court's power to force the prosecutor to bring charges again. That's within the prosecutor's discretion. This ruling leaves it in their hands.
if the witness is unreliable, isn’t that for a jury to decide?
Yes. The verdict was vacated because the fact of the witness' past lies was withheld from the defense and the jury.
It seems like there wasn’t any proof he lied in this case.
How could there be? He claimed that the defendant confessed in a closed room with no one else observing and no recording, and he destroyed his notes. Of course, you could lock him in a room with another detective and then say he confessed to lying about Milke's confession ...