Dr:VR Beta Cases

Case 1

Majority of the Casts don't have names so I'm using the letters of their talents

MonoNeko File:
Boy M was found in the Boy's Restroom.
Time of death is 10:40; After the nighttime announcement.
A knife was impaled in his abdomen.
No other injuries were found.
No signs of any chemicals are in his body.

Alibis:
Girl PD found out while doing the autopsy that the Knife was fake.

Boy O claims that he lost a few of his props while he was on trash duty.

Girl P found a Metal Katana covered in blood near the incinerator. No one in the school owns a Metal Katana.

Girl CA claims that she asked Boy O to record a fight scene for her to practice drawing during breakfast.

Boy S saw someone going to their lab while he was cleaning.

Girl J found a camera in Boy O's lab. The video is blurred but the audio still works:

Boy M: !lear era sporp eht fo emoS !luferaC-C ?!...O yoB
Boy 2 (Killer): ?huH
*STAB*

Suspects:
I don't need to say it since it's quite obvious

Who killed Boy M?
If you want a Hint:
Ask Girl SP about the Video (Direct)
Or...
Ask Boy S about his alibi (Indirect)

You guys can comment your guess (just don't look at other people's comment replies)