Thinking about that flashback scene shown in "Target" during Alpha's rampage. We see the other dead dolls, we see Echo poised in the middle of them asking why they won't wake up, and we later see Alpha with the knife. We do not see Alpha actually killing them.
I'm wondering whether Echo did.
They're in the showers, her hair is wet, almost as though some of the blood has been washed off. It's the sort of Joss twist that I'd almost expect from him.
Mind you, I'm probably over thinking this too much.