Who's the mystery killer?

Just finished ep. 26 one murder  mystery solved and one to go

 Winnie_poo:

Definitly is the eldest Ou son and concubine Qin...they maybe talking something about Xu family and shiyi mother hear it..so for silent her,he killed her...saw some clip for eps 37/38 the elderst Ou son meet with someone and from the back I think is concubine Qin..the motivation for they work together maybe something connection with the child that she lost...

It would be crazy for me to say the child was her and him rather than the Marquis....

Then again, it won't make sense? 

Finished ep 41 and the murder was solved.

Edit- finished ep 42 and the circumstances that lead to the murder are clarified further. 

 Jinxinsiyu:

Crappy writing. It's a good thing the actors are really good.

I guess the writer using her imagination too ... "high". Since its different from the novel pretty much. But if we pretend never read the novel and consider this one not adapted from any novel, it can give us quite good impression about the story. 

And you are surely right about the leads. So much love for them.