We know that usually balefire always prevents transmigration (in the books it's basically a rule without an exception). In his Q&A, RJ stated then that only if a very small amount is used, the DO can theoretically still transmigrate someone, who was balefired anywhere (though apparently already Moiraine's amount of balefire was enough to prevent a transmigration of Be'lal). RJ never indicated at all that this statement would only apply to SG or the distance to SG. Therefore the killer either used a normal amount of balefire, which already made sure on its own that Asmo couldn't be transmigrated (which naturally would make the most sense), or the killer used such a very small amount, but then the DO could still transmigrate Asmo anywhere he died.

As said, likely those surprising RAFO limts, which RJ and BS mentioned, might rather explain, why Asmo couldn't be transmigrated (and then we will likely learn about this, when Asmo's killer reveals the deed). So, what general other limits might be there, irrespective of the question how and where Asmo died?