I considered the possibility that George Sodini, the fitness club shooter, was compelled to do it via temporary possession by the Spirits of Darkness, as I surmise Andrea Yates was driven to kill her children. I found it interesting that the crime had occurred almost precisely 24 hours before the full Moon, perhaps to give Satanists something to celebrate during their gatherings on the following day. However, his blog included statements which indicated that he was ultimately in control of his actions, such as the passage in where he wrote that he had decided against a "shoot 'em up" at his work place, since they had treated him well. This was actually one of the more chilling passages, in my opinion, because it indicated that all that mattered to him about other people is how they made him feel. (Note that after one blog entry, he indicated that he felt better as a result of making the entry, which seemed to consist of projecting his own psychopathology onto others.)
Still, there are a couple of "spooky" passages in his blog. One of these was "something bad must happen," and the other is "death lives!" Both of these seemed to come from a different mind, perhaps from the Spirits of Darkness, which influence everyone to a certain extent, but someone such as Sodini to a greater extent because of his native state of mind, his location on the Earth Grid, and the time of year. Note that he indicates that he planned to stage his attack last summer, and actually did it this summer, perhaps because that's when beings from the etheric "underworld" have the greatest influence.
So, although Sodini still had free will, Satan could very well have played a decisive role in the rampage. In any case, he's no doubt pleased with the outcome.