The Riddler Who Can't Solve Riddles Theory

The Riddler Who Can't Solve Riddles, a song sung by a vocaloid, Kagamine Len.
The song is about a murder that takes place, and they're trying to figure out who the culprit is. There are many theories to this song, and I also have one of my own. It's a bit confusing to comprehend, as I'm still confused myself, but it's all a matter of trying to solve it. [if that's even possible]

Now before I tell you my theory, there is a second part to this song [The Riddler Who Won't Solve Riddles] where Kagamine Rin tells her part to the story, making it even more confusing, yet also putting some pieces together.

"In order for this story to end, everybody must die."

"You don't want it to end? You want to solve it?"

"...But this riddle is filled with so much factual errors."

"There's no chance of you solving it."

As it mentions during the second part, Len and Rin are under a curse. A curse put on them by an evil culprit. I'm going to guess is that this curse is one that draws them to kill. Len to kill with poison and Rin to kill with a knife.

In Len's version, [the first song] he continuously tells Rin to "say his name" because he wants to take the blame for the murder. He is also pretending to be mean to take all suspicion off of Rin. Rin though refuses to turn Len in, for they are most likely friends/lovers/siblings. They have some sort of connection to each other because Rin mentions that Len lost his arm in result of saving her at one time. She feels bad that he lost his arm because of her.

As for the two poisoned glasses, I believe that Len was trying to kill himself and Rin so that they can both be 'free' from the curse put upon them. Rin then decides to kill Len to set him free from the curse as a pay of repaying him for losing his arm for her.

She decides to live with her curse and gives out another riddle. She states that she would trap any person who would try to figure out the riddle in their world. I'm guessing she would give that person the curse to make them suffer through what she and Len went through.

My theory doesn't really explain though who the culprit is. There are lots of theories to who it is and my favorite being:

The culprit is the listener of the song. Because we are listening to it, we are forcing Len and Rin to go through with the murder and sing out the story. Cursing them over and over again. "In order for this story to end, everyone must die."

That is my theory to these songs. There are many more and they are quite interesting to read. Some being more or less the same or make more or less sense. Teehee.

What do you think?

Who is the culprit?