I have a fair number of headscratchers about this game..

[LuckyBlackCatXIII]

When the little girl escapes, Daniel tells the mother: "tell me where she is, there's no telling what horrors await down there!"

Well, did he say this just to get the mother to tell him where the girl is or was he genuinely concerned about the kid?

Personally I believe it to be a mixture of the two. Part of his humanity might have still been there for him to be generally concerned with Elise's well being but I'm sure the desperate part of his character might have also said it just to get an answer from the mother.

Judging by the voice acting I'd say Daniel was indeed genuinely concerned about the kid, but then.. he did know what was going to happen to her soon (torture).

Maybe he didn't know what would happen with the kids? I know that sounds silly but hear me out. From what we know from the torture devices, Daniel only dealt with adults. Perhaps somewhere in his mind he didn't believe they'd torture a kid. From the Remember files we know she had an older sister, maybe he only thought they'd be using the mother and eldest daughter? I dunno, it's an idea but I will agree that it seems odd he would be concerned if he knew what they would do with her.

Also WHY did he kill the girl? He had more than enough strength to easily subdue the kid

He killed the girl simply because he was worried Elise would tell the outrider, Gabriel, what had happened to her and her family (and what was going on in Brennenburg) who would in turn alert the king's men. If this happened there was a chance they would come to the castle before he and Alexander could preform the final banishing ritual. And, from what we got of his character during the "Paint the Man" scene we can see his mind isn't in the right place, he became desperate to stop this (and I'm pretty sure anger that she could ruin all their hard work played a big part of his actions too) and killed her since that was probably the best solution that popped into mind at the time.

Of course we all know how everything then plays off after that!