With as quickly as the media got out there and started talking about what was going on - everyone with a different story, it seemed - the conspiracy theories coming from this don't surprise me in the least.
Now people just grab the story they find most expedient for their cause (and both sides are doing this), show a news snippet to back it up, and claim it's truth.
I believe he acted alone (I've heard reports of as many as three shooters), and the Bushmaster was the long gun he had on his person (the gun in the trunk was obviously a shotgun). Given the caliber of the Bushmaster vs. that of the two handguns, I expect it's pretty easy to tell which gun was used on the victims (hint - the Bushmaster rounds are significantly smaller in diameter).
Now we need to stop sensationalizing this tragedy.

What is the point of rules that are not enforced?