And they shoot at the same time?

The shots occurred in a span of several seconds, not simultaneously.

I don't see anything implausible about a second shooter having Kennedy in his sights, waiting for the initial shots to be fired, and pulling the trigger once he heard the initial shot.

There are a lot of implausible aspects to all of this, but that... doesn't seem like one.

But that needs a bigger conspiracy than just kill JFK.

Either there are two shooters working together from the beginning, or one knows about the other and the other does not.

    But that needs a bigger conspiracy than just kill JFK.

I don't feel like "two dudes who both want to kill the president in a country where it's really easy to get a rifle and there are ~16mil WWII veterans and millions more who know how to use them" is a really big or implausible conspiracy.

What about that seems implausible to you?

As for coordinating their fire, what about that seems implausible?

"I'll shoot first, once JFK reaches point XYZ. When you hear my shot that's your signal to shoot. Be ready and have your finger on the trigger, because obviously Secret Service is going to floor the gas and GFTO ASAP as soon as the first shot is fired"

That seems entirely within the realm of plans two dudes could come up with. I don't think it necessarily points to some larger conspiracy.

People seem to go between lone gunman or giant conspiracy and exclude the middle. It could have been a conspiracy of say four people: two shooters, one insider providing info and cover, and someone behind and planning the whole thing.

Much easier to keep everything quiet too. The difficulty of keeping secrets increases exponentially with the number of people who know it.

Yeah. Given the weirdness of the magic bullet theory, especially if the revelations in the linked article are true, I think this sort of "small conspiracy of 2-4 people" is the simplest possible explanation.

I mean, sometimes a former military guy decides to do some killing and sometimes he has somebody working with him.

https://en.wikipedia.org/wiki/D.C._sniper_attacks

What happened to the third bullet in this scenario?

A lot of sharpshooter/sniper types who have tried it seem to say it's pretty easy. Interestingly they tend to miss the first shot (like Oswald) due to the steeper downward angle.