It sounded from the witness, like the shots came after the scream, but nobody seemed to ask her how long after, from her statement I would estimate seconds, from how she articulated but I can't be sure.
One thing to note is that eye witness testimony is actually one of the worst kinds of evidence. People often mis-remember events and their brain will many times fill in the blanks. Also, time can be difficult to interpret in these types of situations.
This is why I am puzzled. I just can't see a scenario by which she would scream, then immediately be shot dead, unless the reason for the scream was that she was about to be shot dead.
It's possible. But in that scenario, there would have had to be some altercation of some type prior to her entering the bathroom. That could have happened.
Point of fact: the vast majority of murder result in the most logical suspect being found guilty. Largely due to the fact that they are the ones most likely to have a motive in the first place.