I think it's fair to assume that those who possess firearms are more likely to shoot someone than someone who does not possess a firearm.
Just like folks who go to the bank wearing a scream mask are probably more likely to rob it than not.
The bulletin is not very informative
I guess it depends on how you define "possess". If you kill your mother to gain access to her firearms to then commit the murders at Newtown, you didn't really possess them as I would define it. At the time of the murder you did indeed have them in hand but you acquired them through murder/theft. The anti-gunners in public health have been pushing this association since it became popular to get gun research published. The old a gun in the home is 43 more times likely to result in injury and death etc. Statistically discredited but still thrown around often.