Shock factor, I suppose. Last time he saw his twin, he had a knife through his stomach.
That combined with fact that this took place over the course of a few minutes (I know, the year of flashback chapters threw us all off) plus the addition of all the major side characters bursting in (Undertaker, the Dispatch, Elizabeth, and Scotland Yard), he got no chance to speak up before the planted evidence was pinned on him. I think his silence was taken by the cops as guilt rather than shock.
No doubt we'll be seeing some conversations between the twins sometime soon. Might take a few chapters, but we'll get to it. Eeeeeeventually...
But did you see his reaction? He just accepted to leave with the police. He could have been shocked and then try to ask his brother was all this meant, but no...
Non-compliance would have negative consequences in the long run. They found the bottles, and Blavat pointed him out as the perpetrator. Also considering that all of his acquaintances just found out that OCiel was lying about his identity meant that resisting arrest would be like screaming "IT WAS ME ALL ALONG!".
The deck is stacked against him, and he knows better. He knows that the police will either figure out the truth, or he'll figure it out with Sebastian. Abberline does know about his position as Guard Dog, but in the face of strangers, he can't say that. So OCiel needs to be tried.
As for asking his brother, from his little thought process, he knows someone is setting him up. Asking his brother why he's framing him in front of all these people would probably be met with disbelief. RCiel could just spin more excuses and make everyone hate OCiel and Sebastian even more. After all, it's fact that Sebastian DID try to kill him.
So OCiel being quiet and not resisting arrest, lest he lose more allies, is actually a smart move.
Hope that cleared it up a little.
Yeeeeaaaaah, but still! Just going with it and showing no emotion is like saying "I am not agreeing or denying anything, try to prove me wrong!" which does not look like something someone innocent would do...
I think what bard said to Sebastian was some kind of code. They’ve done this before. Idk.
Fighting back would look equally as bad, especially with a majority of the people present against him
Why didn't our Ciel talk to his twin before he got arrested? Instead he just accepted it without saying anything... Seems strange to me since he was completely innocent here. Just because the star guy says it's him, they believe him? Weird...