I would say mostly yes, not always.
- You come upon a mass shooting scene
- Someone has just shot someone else
- That person shooting throws down their gun and throws up their hands
- You shoot them
How do you know you did not shoot someone else who was intervening to stop the mass shooting? In fact it could even be you if the person being shot the first time was unarmed.
Again you seem to be speaking of a situation that would take far longer than the subject "engaging an active shooter" would actually take.
If I were in a public place and a mall ninja carrying multiple firearms opens up on a crowd I don't think I would have any difficulty in identifying who is the actual threat.
The entire engagement would take less time than it takes to type this sentence. There won't be any calvary charging to the rescue before an expended case hits the floor.
If there were any LEO already in the room then they had better have been firing on the same guy before I did.
How long does it take to "throw down his gun and throw up his hands"?
How long does it take to pull a trigger?
If he is in my sights he would not live long enough to drop his piece much less throw up his hands.
In a couple of books written by WW1 veterans they mention how German Machinegunners would continue firing to the very last second, then throw up their hands in surrender. By that time surrender was not an option so far as those they had been shooting at were concerned. The German gunners were lucky if they were shot to death immediately.
Those were soldiers doing their duty, and they paid a heavy price. A mass murderer can expect no better.
Also have you ever studied the drills that government security guards armed with the M4 or similar carbines practice till its second nature?
If the carbine jams they do not try to clear the jamm, instead they drop the carbine and draw their sidearm in one smooth motion, continuing to lay down fire without missing a beat.
Someone dropping a carbine does not mean they are out of the fight.
I ran across that last tidbit in several sources. For some time, late 90's early 2000's at least, Airforce hostage rescue team carbines were built on early type uppers with no forward assist. the reasoning being that any jam of a well maintained AR type rifle would likely be one that could not be dealt with quickly enough. From reports of jams involving the M4 in combat that appears to be true.
Clearing a jam while you have a platoon backing you up, and the enmy hundreds of meters away may be an option. Trying to clear a jam when you are in the middle of laying down covering fire at ranges more likely measured in tens of meters would leave yourself or other swinging in the wind for seconds that seem like hours.