This is fascinating. But, some of us are not familiar with your military terminology. Could you state it in 2 or 3 simple sentences that would explain it to the man on the street? I’ll share it far and wide, if you can.
Here is a video of targets being 'painted' by a laser. Remember - the beam is invisible to the naked eye. Assets on the ground designate a target by pointing the laser at it. Assets in the air(in this video helicopters) shoot at whatever the beam lights up.
www.youtube.com/watch?v=a8LS7QWHyks
It wouldn't make sense to put down your weapon and stop defending yourself long enough to paint a target unless you believed someone else could take out your target from above.
Conclusion - Something was available to take a shot and someone with authority decided to hold fire. Remember - this was a US Ambassador which can be considered the civilian equivalent of a 4 star general. Who would have enough authority to decide to let them die? Hmm...