Well it is a tough situation really!
I think if raunak was the killer, then he would try to hide the evidence not anju, hence I feel anju is the killer, but if everyone remembers, it was both of them that sent simran and vansh to GOA for honeymoon.
Nevertheless i do not understand why would anju kill vansh? i mean what reason could she have?
The only reason i can think of is the prophecy that after the marriage either will die and anju wanted to save simran, but this is really a lame reason!
The other scenario is what everyone is talking about, anju is covering for raunak!
I have another theory!
Raunak killed vansh,( the reason is a no brainer) and is black mailing anju to cover for him because he has anju's brother and would kill him if she didnt help!
this is the most logical one i can think of, which also shows that anju is still not evil, just helpless!
Opinions?!