[MassExodus]

It's a lousy fake.
One of the bigger mistakes novice PhotoShoppers make is not knowing when to "degrade" their own images.
The biggest issue, aside from perspective, is that the "shooter" is too sharp.
He needs to have the same kind of digital noise or blurryness applied to him as the spectators originally suffered.

10% Gaussian blur would have completed this photo.

[MassExodus]

.5% Gaussian blur added some darkening to match the folks in the background.

I'm no longer totally convinced it's fake having looked at it in Shop, the lighter guy in the forground could have been because of the flash...

[D-fendr]

The difference in sharpness could be due depth of focus. Or perhaps motion. Though in the latter case you'd expect the gun at least to have as much motion relative to shutter speed.

I looked at it magnified greatly and don't see obvious pasting. If it is a composite it's much better done than some of the others we've seen.

It looks like there could be an ejected shell above the breech. I don't know what the black splotch below the shooters left hand is though.