How do they know the weapon wasn't from 'Operation Wide Receiver'?

"Family of Murdered Border Agent Lashes Out at Holder"

It's not hard to feel bad for Brian Terry's family but how do they know the weapon that killed their son wasn't one from the Bush administration?  After all, it was Bush's program, 'Operation Wide Receiver' that began selling those weapons to Mexicans.  The ATF under Holder just continued what Bush started.

Maybe they should direct some of that anger toward Alberto Gonzales or Michael Mukasey.  Of course if they did, you wouldn't be reading about it on Fox.