I don’t think echos or reverberation effect following the initial muzzle blast is the answer to this “back to back” perception of a significant majority of witnesses hearing the spacing of the last 2 shots.

If this phenomenon is happening then should not there be that effect for each of the 3 shots resulting in witnesses thinking they heard 6 shots and the spacing would be 1.(2)…..3.(4)..5.(6)?

If the sound they heard was the impact of the bullet on the skull, they would not have heard that on the earlier shots. If the sound was the shock wave of the bullet, each bullet had a different trajectory so it is plausible that they could have only heard a distinct double sound for the third shot based on where they were standing. Another plausible explanation is that they heard a double sound for the earlier shots and simply did not remember it. I lean toward the third explanation. Witnesses just aren't very good at perfectly remembering every detail of the things they saw and heard. Out brains are not equipped with DVRs. We tend to remember bits and pieces of events, not the entire event.

The following article explains the auditory issues much better than I can:

https://biologyinsights.com/gunshot-audio-muzzle-blast-shock-waves-and-health-impact/

Or, if it was a conspiracy, then why did JFK have to be terminated and who profited and did their organization continue  to exist or have they all died.

From my perspective, the only one responsible for the assassination died a little more than 24 hours after JFK was killed. No one else will ever be identified as complicit in the assassination.

They didn't fire any shots that day, but the Secret Service killed him through incompetence.

"After the shooting, one of the secret service men sitting down in the car in front of us pulled out an automatic rifle or weapon and looked backward. However, all of the secret service men seemed to me to respond very slowly, with no more than a puzzled look. In fact, until the automatic weapon was uncovered, I had been lulled into a sense of false hope for the President's safety, by the lack of motion, excitement, or apparent visible knowledge by the secret service men, that anything so dreadful was happening. Knowing something of the training that combat infantrymen and Marines receive, I am amazed at the lack of instantaneous response by the Secret Service, when the rifle fire began. I make this statement in this paragraph reluctantly, not to add to the anguish of anyone, but it is my firm opinion, and I write it out in the hope that it might be of service in the better protection of our Presidents in the future" Ralph W. Yarborough

Some not, not all of the Secret Service agents apparently either didn't hear or did not recognize the first shot for what it was. They believe that JFK was hit by the first shot. It has always been puzzling to me why they didn't respond to the first shot but seems to be the case. Altgens 6 shows some of the agents turning to the rear in response to the second shot which is the first one to strike JFK. Clint Hill only remembers hearing two shots and he reacted when he saw JFK had been hit. The next shot he heard was the head shot as he was racing to the limo. I heard him say that he had been told there was an intervening shot that was fired while he was trying to get to the limo but he has no memory that, with good reason. There was no intervening shot. The shot he didn't hear was the first one. The only occupant of the limo who recognized the first shot for as a gun shot was JBC. He knew instantly what it was and according to his account, he immediately thought it was an assassination attempt.

So why did the others as well as some spectators not recognize the first shot. Some said they thought at first it was a firecracker. Others thought it was a motorcycle backfire. We are left to guess as to why others didn't either not hear or recognize the first shot? My own guess is that the motorcycles accelerating coming out of the sharp turn onto Elm St. created such a roar that it muffled the sound of the gunshot. I have no way of proving that. Just an educated guess.

The agents who believed JFK was hit by the first shot are giving themselves the benefit of the doubt because that gave them less than 5 seconds to react between the first shot and the fatal head shot. Those of us who believe the first shot was the missed shot believe there was actually more than 8 seconds between the first and last shot, varying that time frame based on when we believe that first shot was fired. My own belief is there were almost 9 seconds between the first and third shots. Had any of the agents on the running board reacted to that first shot, they might have reached JFK in time to keep him from being hit by the fatal headshot. Bill Greer was in the best position to prevent the assassination as the driver of the car but I read recently he was only supposed to do that on orders from Roy Kellerman. Had Greer immediately sped away, it's doubtful Oswald could have hit JFK with his follow up shots. Unfortunately, all the agents had to make split second decisions and it is easy to second guess them, but not knowing what they actually saw and heard, I'm not ready to say whether they should have acted more quickly than they did. 

They didn't fire any shots that day, but the Secret Service killed him through incompetence.

"After the shooting, one of the secret service men sitting down in the car in front of us pulled out an automatic rifle or weapon and looked backward. However, all of the secret service men seemed to me to respond very slowly, with no more than a puzzled look. In fact, until the automatic weapon was uncovered, I had been lulled into a sense of false hope for the President's safety, by the lack of motion, excitement, or apparent visible knowledge by the secret service men, that anything so dreadful was happening. Knowing something of the training that combat infantrymen and Marines receive, I am amazed at the lack of instantaneous response by the Secret Service, when the rifle fire began. I make this statement in this paragraph reluctantly, not to add to the anguish of anyone, but it is my firm opinion, and I write it out in the hope that it might be of service in the better protection of our Presidents in the future" Ralph W. Yarborough

Hi Everyone-

I did a deep dive into the so-called Babushka Lady which I think many people here would find interesting.

Not really. One thing this forum has no shortage of is silly theories. I suspect you are just trolling with this one.