Go to the local County Courthouse. Chat with a DA, and assistant DA, a Baliff, a Judge. Ask them what they think causes most murders -- a list of the things. If one of them even mentions porn -- without you first clueing them -- I'd be surprised.
of course we know that all crime is really caused by poverty.
listen to the the jail interviews that have been played by
Dr.Dobson featuring Ted Bundy or David Berkowitz (aka "son of sam")It's good food for thought. I believe the 3rd part
of the Berkowitz one is on Focus on the Family tommorow.
I don't think porn is the sole cause of sex offenders and murder, but is often a contributing factor.