Couple of things bother me about the shooting.  At 100 yards, it is very difficult to hit anything with a handgun.  I cannot help but wonder how the woman was hit twice.  Regarding trajectories, handguns do not have the range of rifles, but at only 100 yards the vertical drop of the bullet was likely not more than a foot or two.  This means that the bullet(s) had to traverse the forested region.  Since the handgun bullets could not penetrate anything substantial, we are led to believe that open spaces through the forest were present and that the shooters may have been able to see the woman.  Also at 100 yards, the shooters should have heard a loud cry for help. 

But mostly all we can do is speculate because we are not privy to all the details.  I am confident that the DA got them for the maximum realistic charges because that's what DA's do.