Whether or not there has been a conspiracy depends on your chosen definition, as well as how you view the Constitution.
Did those with an anti-gun agenda and various media outlets intentionally and collectively manipulate facts, take advantage of ignorance, and tailor their promotion of events in an effort to encourage erroneous assumptions, control common perception, and create the beginnings of division and disorder within the population?
Was their action prearranged in order to quicken response and better take advantage of the next big shooting?
Is every opportunity taken to refocus attention back to an emotional event; the facts of which are deliberately avoided and left to the imagination?
I believe this all to be true, and why wouldn't it be? It's a good plan. If you've got an agenda, it stands to reason you'll do whatever is in your power in order to steer toward it. If you know it will be helped if built upon the foundation of tragedy (this can nearly always be true), why would you not take advantage of such an event?
Clearly, you believe in your cause, and when you truly believe in a cause, it becomes easier to justify the methods used to support it.
The best way to control a person is not to lie. It is better to strategically leave blanks for them to fill in, while making sure the information most easily accessed meets your approval. That can be entirely literal, when adjusting a person's opinion, or more abstract; dealing with their basic perceptions.
There is no need to manufacture a shooting. They happen every now and again. Use the time in between to be sure you are ready to capitalize upon the next one.
Anything is possible, but the people with an anti-gun agenda, for the most part, truly believe in that cause, or they believe in the accumulation of power that such regulation allows.
The "other guy" is rarely the "bad guy". Most of the time, he's just doing what he thinks is right, regardless of how negatively you may view his ideas and actions.
The idea that the government may have created a problem to solve by recounting an event that did not occur, or causing that event themselves, while seemingly reasonable (if terribly paranoid), is flawed. It is not likely that anyone in Washington would do such a thing, and even if they did, any secrecy wouldn't last long.
"The Man" is not nearly as clever or well organized as people like to imagine. Leave that nonsense to the movies.
Cheers,
Kennith