In his sentencing, as transcribed by GamePolitics, Lorain County judge James Burge intimated that he believes -- "as a human being ... and not a jurist" -- that gaming can elicit similar physiological responses and addictions as some drugs (sound familiar?). He further decried the creation of a delusional environment. The quote that's currently making the rounds is, "I firmly believe that [Petric] had no idea at the time he hatched this plot that if he killed his parents, they would be dead forever." In other words: Petric didn't realize there are no respawns in real life, according to Judge Burge.
Of course, attributing Halo 3 as a causation of these crimes is probably reaching, especially when most of the other 6.4 million who bought the game seem to be of sound mind. We're no psychologists, but to us it seems this is about the wrong mind and the right catalyst inciting the most heinous of actions -- whether it be Master Chief, Niko Bellic, The Beatles, or a German Shepherd.