Yellow Submarine Murder Mystery

Okay so I read the prompt and of course, my morbid, cynical mind immediately thought, murder on the submarine. Sixteen kids and a teacher all on a sub, and someone gets brutally murdered. We have to figure out who did it. So our victim will be Hannah. Just for laughs since she's my best friend. (RUDE -Hannah) (Lol I love her...)
So we all get onto the sub and we go around and look at everything. Of course it isn't very large but we don't really need a lot of space for all of us. It was late when we got here so we eat dinner and then retire to our beds for a long night. When we wake up in the morning, it's very quiet. A lot of kids are already out of their bunks and looking for breakfast, I assume. I roll out of bed and see that Hannah's bunk is empty. It's not like her to get up late so I don't think anything of it and I proceed to the breakfast room. Everyone is sitting at the long table and talking quietly. I glance around and notice that Hannah isn't there. Maybe in the bathroom, I thought. I sit down and ask Jessica Garber, whom I'm sitting next to, "Have you seen Hannah this morning?" and she replied, "Someone killed her."

I stare at Jess in shock. I felt the tears welling up inside me and I couldn't hold it together. I started bawling and I asked again and again if she was serious. She told me she was and that if I wanted to know for sure, she was in the command center of the sub. I agreed to go and I followed her up there. I saw that they had placed a sheet over her and that was all I needed. I turned to Jess and I asked her who did it. She said that it was a unanimous vote that Hudson, our beloved teacher that had brought us on this amazing trip, had done it. I didn't think so but I could never be sure until three years later.

I visited Hannah's mom and dad. They had kind of turned her room into a place of peace for her friends. I visited often but this time I noticed something. Hudson had had class pictures taken outside the sub before we left. We had each received a photograph. I had long since lost mine in the move to college and so I never noticed it before. In the picture, there was a shadow next to Hannah. She was standing on the end of the front row and there was a dark smudge on the picture. I tried to wipe it away but the spot wouldn't budge.

There had been a ghost on the sub with us, all of those years ago and it had killed my best friend. One by one over the course of the next six months, my graduating class started to die in mysterious ways. The police labeled them homicides by a serial killer but it was a demon that killed them. Everyone else is dead. I'm the last one. I'll be gone soon so I needed to tell the truth about what I've learned. Please, if you read this, if I'm not already gone, don't come for me. It is my fate. I am to die at the hands of the Submarine Demon.