Execution stopped

Part 1: Her execution.. stopped...?

We shall pretend that we went through the prologue, Rantaro died, and they're finishing the trial and Kaede is about to be executed.
Kaede's neck is the wrapped around and she is pulled away from Shuichi, Shuichi reaches for her but he fails. Her execution then starts and Shuichi yells, "Wait! Monokuma stop the execution! I want more investigation time. And I want in the secret room behind the bookshelf."
Her execution then suddenly started to slow down then, it went to a stop. The n00se around her neck came off and she dropped onto the piano she was on. The Monokubs get her down and they all go back into the trial room.
Monokuma then speaks up, "Everyone, sorry for the inconvenience. Shuichi here wants to stop the execution and have more investigation time. I will only allowed this once because of the juiciness~ So I shall unlock it."
He takes them all in front of the secret bookshelf and opens it and unlocks the secret room.
The students walk in and see a monopad on the table in there, while Shuichi is carrying Kaede because of her weak state.
"Hey, Monokuma," says Shuichi. "Turn on the monopad and show us what's on it."
Monokuma turns on the monopad and plays the video that awaits them. The students watch it quietly and are shocked by it. Rantaro was the Ultimate.. Survivor...?
Shuichi speaks up. "Thank you, Monokuma." The students start to look all over the place for any other clues and then Kirumi looks in the trashcan and spots something...
Kirumi then exclaims, "Everyone, please gather your attention. I have found something in the trashcan."
Inside the trashcan.. There is another shot put ball. Kirumi grabs it and puts it on the table. Shuichi picks it up and starts to inspect it and sees the pink fiber on it.
"Wait a second.. This fiber...", he says in a whisper-like voice. "It's the same color of Kaede's vest..."
The students pass it around and look at the fiber and look at Kaede's vest and agree with him. They then start piecing together the events in order. They find out what happened, but not who done it just yet.
Then the announcement started to play. Monokuma told them to go back into the trial room and go to their designated podiums. Shuichi asked to carry Kaede because of her weak-like state and Monokuma agreed annoyingly.
Shuichi starts, "So, may I present the case in the correct order now that we have it?"
The students exchange looks and nod. Shuichi then starts to go over the case, but then he gets to the part where Kaede's shot put supposedly hit Rantaro.
"Instead of Kaede's shot put hitting Rantaro.. It missed him. He must've been shocked by the sudden occurrence.", Shuichi says. "The mastermind has seen all of this and also knew about the camera intervals due to the cameras around the school. The mastermind then would come out of the bookshelf and hit Rantaro in his skull with their own shot put." He adds, "After doing so, they took the monopad and Kaede's shot put and threw Kaede's shot put in the trashcan and left the monopad on the table."
"Hey, Korekiyo. I have a question.", Shuichi states.
"What is it?", Korekiyo replies.
"Who was in the dining hall with you?"
"Kirumi, Miu, Tsumugi, and I."
"Did any of you leave?"
Korekiyo then says, "Yes, Tsumugi left for the bathroom."
Shuichi then goes into a thought and then he looks up and...