Who wrote the two Japanese hostages case story? Islamic State?

Who wrote the two Japanese hostages case story?
The Media said, "One Japanese hostage was killed."
And also said, "Islamic State wants to exchange the Japanese Keniji Goto  for the female Iraqi hostage.
At first Islamic State demand 200 million $ to Japan.
And now they change the request.
Very strange.
Why?  I don't know.  
Now We must change the idea of the two Japanese hostages case.
We must suspect the organization of sending soldiers to Islamic State in Japan.
The story of this time isn't simple.
If the hostage come back Japan, he must tell the truth not only Japan but also the world.