I may b wrong
Riddhima jise pakregi woh kabir hai...He must have come to meet or interrogate ya jo bhi woh ek cock and bull story banayegii. May b he had burnt the picture.Siya agar culprit hai vi cvs usey utni jaldi nhi pakarwayegi....May b its Kabir who has burnt the picture.
But he will make her believe that he had come for any other reason.
And the person who has caused the blast is someone deadly. Ishani ho ya Siya they will not b caught red handed atleast by Riddhima so easily.
We cannot even outrule Ragini to b the masked identity. I dont know if my theory is logical or not.just tried to gather the piece.