The lawsuit alleged every possible reason under the sun, from defective design to failure to warn to you name it, in hopes that something would stick. You can read all about it from the anti-2A perspective at the Brady campaign site, and perhaps get a sense of who and what was behind the suit. The Brady united site has information on the suit from their perspective, but I won't link to it here. I have not read who removed the mag from the gun, but would not be surprised to learn that the shooter had done so.