The riddle solver who can't solve riddles

Yes, I know that the title of this post is a bit weird, but I shall explain.The riddle solver who can't solve riddles is a fun vocaloid (If you don't know what a vocaloid is click here) that I listen to most days. I find it very funny, in a creepy sort of way.Oh, and by the way, it's in japanese. Here:











The english translation to the lyrics:

The first riddle is why was he alone in his room
Drinking poisoned wine?

Quietly listening to the detective
the detective continued in front of the girl

The reason is simple, at that point and time
He was destined to die

So, who is the culprit?
You know the answer to that question
Since it happened in front of your eyes
So, who is the culprit?
even if you don't say, I will answer for you
So this crime will end

The second riddle is why did they fall into the ocean
And was the culprit really among them?

The girl grabs the knife hidden in her pocket
The detective doesn't realize, and continues talking

One mistake in my plan
Was the detective dragged into this

So, who is the culprit?
The detective easily hits it out of the girl's hand
Her last resort
So who is the culprit?
Come, the name of the person in front of you
Say my name!

I really
Didn't want you to find out
I will be merciful
If you want to run, hurry...

So, who is the culprit?
There may be more than one answer
But the answer is about to disappear
So, who is the culprit?
Hurry, if you don't answer quickly
My hands are going to kill you
You don't have much time

So, who is the culprit?
You know the answer to that question
Since it happened in front of your eyes
So, who is the culprit?
the person standing in front of you
Come, say that person's name
My name!

Please comment telling me what you think the answer to the riddle is. If no-one can work out who the murderer was, then I'll tell you.