How Petyr's "trial" could've gone
* Sansa accuses Petyr with no proof of trying to poison his wife's son. He reminds everyone that Sansa was accused with no proof of poisoning her husband's nephew.
* Sansa accuses Petyr of seducing & then murdering Lysa. Petyr reminds everyone that Sansa told the Vale Council that Lysa called her a whore, tried to kill her, then committed suicide. "Did you tell the truth then and are lying now or did you lie then and are finally telling the truth? You're such a first rate liar it's hard to tell. Ask Mycah. You remember the butcher's boy, don't you, Sansa? The first casaulty in your game of thrones. Your direwolf Lady was the second casaulty since you always seem to get burned by your ambition and then blame others for your misfortune. You want to be Queen and won't let anything or anyone get in the way. It's all you've ever wanted. Returning home, reuniting with your family, nothing compares to that feeling when you're the one setting the pace and everyone has to fall in line behind you."
* Sansa accuses Petyr of trying to persuade her to kill Arya. Petyr tells everyone that Arya has a bag full of skinned off faces, proving she's a Faceless Assassin. Thus it makes sense to strike first in case she's not even the real Arya or Westerosi.
* Sansa accuses Petyr of trying to gain control of the Vale. Petyr tells everyone he offered for the Vale army to fight Ramsay's army but Sansa refused, didn't tell Jon about the offer, waited until the majority of those who were fighting in Jon's name might be too late to be saved then sent a letter to him to bring the Vale so she can claim victory.
* Sansa & Arya accuse Petyr of plotting against Ned Stark. Petyr tells everyone that Ned knew Cersei's children were bastards born through twincest and was going to give the Lannisters time to escape Westeros before telling King Robert which is treason then lied under oath proclaiming Joffrey as the new King in order to save Sansa, who only needed to be saved because she went behind her father's back to inform Cersei that he had gotten a ship to get both his daughters back to Winterfell. "I got you out of King's Landing. I saved your life."
* Sansa accuses Petyr of selling her to the Boltons. Petyr tells her that Robert beat & raped Cersei but that didn't mean she was sold to him. And that she too orchestrated her abuser's death via animals. He says Sansa willingly married Ramsay and not once did he threaten or force her to it. "You chose the Lannisters and then they abused you. You chose the Boltons and then they abused you. Your brother Robb fought the Lannisters and it cost him his life. Your brother Jon fought the Boltons and if I had been a day later with reinforcements he would've been a goner as well. Who will you choose next and how many thousands will die because of it?"
* Petyr reminds everyone that Jon is the King of the North and doesn't know and hasn't consented to his execution. The trial should wait until his ship arrives in 1 1/2 months. Actually by late s7 Daenerys was the Queen of the North so the Starks have no authority to execute the Lord Protector of the Vale and really overstepped.
