Murder isn't the way to awaken the mangekyou, the real factor is emotional shock (as is revealed by the second hokage if memories serves)
How did seeing your whole clan get murdered not suffice as emotional shock you might ask ... shit writing is the answer you seek
Shikamaru really got the short end of the stick with this whole situation. He was basically forced to be Hokage because there isn't anyone else smart enough or strong enough to do the job. He's gonna be pissed if/when Eida's thing wears off.