it's not gun ideology when you omit facts you didn't have time to ascertain. the full enabling idiocy of nancy lanza wasn't evident the day after newtown, either.
The article about the NM shooting said he got the gun at home. Further details will require more detailed investigation, and it would be inappropriate for Reuters to speculate. As for where he learned to modify it, why is it surprising that a 12 yr old would have access to tools, know how to use them, and have some thoughts on what to do with them?
It doesn't matter how the guns were obtained. It's taken as a given that there are so many fucking guns in this country that anyone can get one at any time for any purpose. There's no point to even discussing how or why someone obtained a gun until we enact laws that actually force owners and businesses that sell them to be accountable for what happens with a gun -- i.e., some form of strict owner/product liability. Until then, it's (quite literally) business as usual in America.
You know, like REAL journalists do.