The companion does confirm it was the Black Ajah.  My guess is Alviarin, If it wasn't Alviarin then we were never going to know, since she is the only BA we really can suspect.  I agree that the scene was most likely meant for the reader to suspect Elaida.  Though this could fall into RJ'S it's obvious stuff, like he insisted with who killed Asmo.

Edited December 9, 20196 yr by Sabio

The who-done-it is understandable as it wasn’t clearly stated or implied, but I was pretty surprised that anyone who was into the book enough to come to this forum and actually post here could not see the reason behind having Sahra killed. That was so clearly developed in the plot as to be obvious, and anyone who doesn’t understand that needs to read it again. Anyway, I’m going to give it another read after New Spring and see if I can shake anything loose on who did the deed.