Part 100: Super High-school Level Update #90
Chapter 4 Trial / 18 (Youtube via Polsy) 
Yep.
The person who killed Oogami-san is Oogami-san herself.
...Ulp!!
W...What did you say...? Oogami herself... is the culprit...?
D...Does that mean... it was suicide?!
I can't believe it. I'd believe I could fly before I'd believe it...
I also can't believe it. No, I don't want to believe it... But however you look at it, it's the only explanation that fits everything. Oogami-san went to get a bottle of poison. Then, she drank directly from that bottle... ...It's because she wanted to end her own life.
Then there's the unsolvable locked-room mystery... It figures we couldn't figure it out.That's because...
The victim locked the room / Togami locked the room / Monobear locked the room
That locked room... was created by the only person who was inside the room. Oogami-san herself.
She probably didn't want anyone to interrupt her, so she blocked the door. Oogami-san drank the poison she brought to the locked room, and breathed her last breath. Then, the bottle of poison rolled on the floor and remained there until the room was broken into, but... After the room was unlocked, a certain person took it away.
Asahina-san... it was you, wasn't it?
Uu... Uuu...!
You did it to interfere with the investigation, didn't you?
When we found Oogami-san's body, you remained standing near the door... That was because you already knew Oogami-san was dead. And then... Since the bottle of poison rolled to somewhere near the door... That was when she picked it up, isn't it? I was in a state of shock after finding the body, and Kirigiri-san started checking for signs of life, so we couldn't see her...
Furthermore, when I think about it now, Asahina-san's actions after finding the body were a little strange...
I must... call the others... I'm going... to get them...With shaky steps, Asahina-san left the recreation room.
You said you were going to call everyone, but... Your true goal was to go to the chemistry lab so you could to exchange the containers, wasn't it.
When you got to the chemistry lab, you went straight to cabinet A, where protein cans are stored. You poured the contents of one of the protein cans into the empty poison bottle you took from the recreation room... Then, you took just the empty protein can, and left the chemistry lab. ...That fits perfectly with the footprints you left behind.
Then you hurried and called everyone, and when you returned to the recreation room... I... brought them...
Whoa!! T...the Ogre!?
Oh my... That is certainly a dead body.
I see. So Sakura Oogami has been killed...
When everyone's eyes were on Oogami-san's body, you silently dropped the protein can in the crime scene.
............
I should have noticed... The Asahina-san I know would rush to Oogami-san's body faster than anyone else... The Asahina-san I know... wouldn't leave Oogami-san's body alone for a second...
............
Oogami-san took her own life. In order to hide that truth, Asahina-san took action to disrupt the crime scene. As long as the truth remains hidden, it didn't matter if you took the blame. That's probably what went through your mind... That's why you deliberately left careless evidence behind, wasn't it?
Footprints in the powder, an empty poison bottle... All evidence of major importance.
So, Asahina... messed with the crime scene to make it look like she was the culprit...?
............
You're... wrong...
Wrong, wrong, wrong, wrong!! I killed her! I killed Sakura-chan!!
...Asahina-san, that's enough. It's... over now.
No! It can't be over!!
IT'S OVER!
No, I guess it's up to me to end it now...
I will end it right now...! Phase 14 (Youtube via Polsy) 
CLIMAX INFERENCE
THIS IS THE TRUTH ABOUT THIS CASE!
This case began when Oogami-san invited several people to the recreation room.
The people she invited were Hagakure-kun, Fukawa-san and Togami-kun.
The first person to head to the recreation room was Fukawa-san.
Fukawa-san entered the recreation room ahead of everyone else, and hid herself in a certain place.
It was the recreation room locker... Fukawa-san went into it to hide.
And then, she watched Oogami-san enter the recreation room from inside the locker.
Next, Hagakure-kun entered the recreation room.
He thought Oogami-san wanted to kill him, and lost his self-control...
Without thinking, he hit Oogami-san's head with a Monobear bottle that was in the room.
Thinking he killed her, Hagakure-kun proceeded to mess with the crime scene.
He used a magazine that was lying on the table, and faked a dying message left by Oogami-san.
He wrote someone's name in it.
"FUKAWA"... That is, by writing Fukawa-san's name in the magazine, he thought he'd frame her for the murder.
But, the actual Fukawa-san saw everything. She saw it from inside the locker...
She rushed out of the locker, and hid the magazine that was tampered with in the magazine rack.
But she made a little blunder. That blunder was...
When she put the magazine back in the rack, she placed it upside down.
Right after that, Fukawa-san noticed Oogami-san, who opened her eyes...
She lost her consciousness after seeing Oogami-san's blood.
...And as a result, her personality changed to Genocider Syo...
But as soon as she opened her eyes, she saw the blood-drenched Oogami-san in front of her...
...and lost her self-control.
Then, just like Hagakure-kun before her, she took a Monobear bottle and hit Oogami-san on the head.
That's why Oogami-san' body had two wounds on it.
Thinking she killed Oogami-san, Genocider Syo proceeded to clear the evidence.
She got rid of the shards from the bottle she just smashed, as well as the queen Monobear figure.
Oogami-san was now hit two times with the same weapon...
...But she was still alive even after that.
So, what was the true cause of her death? That was...
...Poison she herself brought from the chemistry lab.
She blocked the door, drank the poison when no one could enter the room...
And then, she died...
After that, we discovered the body...
We had to break the window on the recreation room's door in order to unlock the room.
But, at that time, there was someone who already knew Oogami-san committed suicide...
That person stealthily grabbed the bottle of poison that was lying on the recreation room's floor...
And then, when we weren't looking, replaced it with a can of protein.
By doing that, they tried to attract our suspicions to their own self.
They did it to make us reach the wrong conclusion in this school trial.
And the person who did all that...
Asahina-san... It was you...
Chapter 4 Trial / 19 (Youtube via Polsy) 
That's... the truth behind this murder.
Uu, wahhhh...!!
Oogami-san... took her own life. In order to hide that truth... Asahina-san told us she was the culprit.
............
That is... the truth?
But, Naegi... how could you...? How could someone worthless like you reach this truth...? A truth... I couldn't reach myself...!
Eh? No... I didn't mean...
...You still don't get it, do you? Humans don't always act in calculated and logical ways. That's why dealing with human beings is difficult. You never understood that fact. That's why you couldn't see the truth.
Keh...!!
I did warn you before, didn't I? Holding people's feelings in low esteem could come back and bite you...
............
Calm down... the general mood indicates we've reached some kind of conclusion...
But aren't you forgetting something? You still haven't voted!
Oh, right. There's that, I guess.
You really did forget?!
Uu... how depressing... But... voting is traditional, so let's get on with it. I know it's just a bother, but please use the switches in front of you and vote... Who'd be voted as the culprit, I wonder... Will that answer be true or false... What will it be...?
We're back to voiceless sprites now. I hope you enjoyed the videos!
You voted correctly... ...That's right, the person who killed Sakura Oogami-san was Sakura Oogami-san herself...
...The end.
I see. It really was the truth... But, I still don't get it...
Asahina... Why did you try to hide Oogami's death...? If you succeeded, you would also be executed... Why did you do that, even though you knew that?!
Yeah! It was dangerous! We almost died!
T...That's exactly why...
...That was what I was after!! ...Eh? I mean, Sakura-chan died... Because we all... pushed her to the corner... We all... killed her... That's why... I couldn't let her die alone, could I!
Don't tell me you...! You wanted to drag us all in with you!? We must atone for our sins... I killed her... and so did all of you... We should all pay for what we did...
A...Are you serious?! What's up with you...?! If you don't get it... I'm going to explain. I'll show you what kind of despair Sakura-chan fell into when she died! Take a look... at this.
"I have fallen into utter despair.
I am in despair watching everyone mercilessly fighting each other.
When all there is left to do is wait to be killed, I may as well take my own life."
W...What's that...?! I found it on the floor in front of the recreation room... It's Sakura-chan's... suicide letter. Oogami-san's... suicide letter...? Now that I think about it, there were signs it was going to happen even before...
It happened right after Genocider attacked me... When Sakura-chan heard about it, she got mad and ran out of the infirmary. It was after that...
I ran out of the infirmary myself, chasing her...
Calm down, Sakura-chan... I'm fine...!
I cannot calm down...! I do not mind if they hurt me... It is all my responsibility... But for you to get hurt... just because of what I did...
Because of what I did... Because you tried to protect me...
My best friend wound up getting hurt!!
S...Sakura-chan... It is my fault... It is my fault... that friends are killing each other... It is all... my responsibility... Sakura-chan... felt responsible for everything. She said... it was all her fault... So... she must thought she could do something that would make everyone forgive her... And so, she invited the three of you...
You invited those guys...? You should cancel it! It's too dangerous!!
It is fine... I just want to talk to them. Talk to them...? About what...? ............ I really don't think you should do it. If they all attack you at once, even you...
Asahina... Do not be confused. They are not our enemies...
They are... our friends. S...Sakura-chan... She must... have believed what she was saying... She believed it with all her heart... She thought she could explain it to them... Make them understand we're all friends... But instead... ...Instead!!
You guys just stepped on her feelings... in the worst possible way...
N...No... That was just an accident, 'right? Don't try to discard what you did by calling it an accident!! She believed in you... and you didn't even try to listen. You just got her to kill herself... without a worry in your heads... Sakura-chan... fell into despair because of you!!
That's... what this suicide letter means... If all that was left for her was wait until someone tries to kill her again, she... That's how much she was cornered...
Sakura-chan! What happened? You're wounded!!
A...Asahina... You came... Wait here, I'll go get a first aid kit...! A...Asahina... Eh...? I am... happy I could meet you here... W...What's wrong, Sakura-chan? What are you saying...? ...I...I have a request for you.
...A request? Protein... Can you go get me some? Would you help me...? Y...Yeah... I got it. Wait here, I'll be back in a second...! That was... the last time I spoke to Sakura-chan.
I went to the chemistry lab to get the protein, but there was powder scattered all over the floor... And then I realized... I realized that Sakura-chan took something out of the poison cabinet... I ran back to the recreation room as fast as I could... But... she was already...
Sakura-chan!! Open the door! Let me in!! ............ Why... W...WHY...?! Why does Sakura-chan have to die?!! Sakura-chan was human. She had weaknesses... If you stabbed her, she bled. If you wounded her, she felt pain. That's the kind of regular, weak human being she was... And yet... Everyone pushed her around... You even hurt me when I tried to defend her, and that just made her burden heavier...! And then, even I didn't notice in time... Asahina-san... We all killed Sakura-chan... We all... cornered her and killed her... Why do we get to live after what we did?!! And so... you tried to drag us all down with you... You tried to make us choose the wrong culprit at the school trial on purpose... If we all paid for what we did by dying, it would settle the score... But... I failed to do even that... I couldn't do anything for her after all... I... am too ashamed to even be called her friend anymore...
Hey, I realise this is an awkward moment to butt in, but...
It's taking way way way way way way too long!! You talk too much, and I'm falling asleep!
...By the way, Asahina-san. Do you really understand what Oogami-san thought of when she died? What...? I mean, most of that story was your personal interpretation of the situation, wasn't it? Your interpretation based on that suicide letter... Of course I understand her! Me and Sakura-chan... we were...!
What I'm trying to say here is... That you're basing it all on the wrong thing.
You should have been looking at this thing right here...
W...What is that thing? Isn't it obvious? It's a suicide letter. The one Oogami-san wrote. S...Suicide letter...!? But Asahina-san already...!
Oh, I wrote that one. This one right here was in Asahina-san's room. It's even addressed to her!