I don't thing those are reports, but interpretations of the terrible quality photos. But, you can see a dark strap across his chest starting at his right shoulder. Very possible he had the rifle across his back. Or, as I mentioned in post #401 (see link there) he could have had a "takedown" rifle under his shirt and pants.
I'm leaning toward a short rifle on his back. At 9:30 pm, not too many people in the mall and most aren't looking at his back. If he had it in a black cloth case, it would be essentially invisible. Just my opinion.
The man running the investigation said he entered without the rifle and came back. See my post above yours and the linked article.
That is not speculation and one would think the person who said that probably knows the most about the incident at this point?