Just because your mind, (or someone else's) is imaginative and is able to come up with stories you find satisfying/compelling doesn't mean they are likely or true. In the same way that our brains make pictures out of clouds, they make patterns out of events.
Conspiracies can exist (such as e.g. the police cover up at Hillsborough) however lies of that magnitude are extremely difficult to keep, and everyone who had been there knew the police and media were lying. When you are talking about multiple people knowing about doing something so unethical, you are risking them uncovering it or telling someone else etc.
Then you have to think why would 'they' need to do this? There are lots of shootings anyway. And it would likely be ineffective (none of the previous tragic mass shootings have resulted in gun control).
The thing I find interesting about conspiracy theories is there is an underlying order to the world. It's disturbing because the baddies are in charge, but there is hope that they can be overthrown by the special people who have found out the 'truth'. Whereas the non conspiracist doesn't have to handle the idea of baddies on charge but does have the disturbing belief (I'd say truth, I suppose) that it doesn't matter if those "in charge" are well meaning (though often flawed) they cannot foresee and prevent all horrible events.
Maybe you were just stirring, but if you truly believe that this is possible or likely, I think asking yourself some questions about whether a conspiracy is necessary to explain the events, and if not, then the simplest explanation is probably the most likely. If your brain wasn't the patten machine that came up with this explanation, i.e. if you came across the idea somewhere, then consider the profit motive of who is spreading this stuff - who is getting the clicks/followers/subscribers/views by spreading sensational takes on current events.