Update: More here from Joshua Frens-String. Two big questions at this point are whether the shooters knew they were shooting at Americans (some American officials have been quoted as saying, Yes, they definitely did, but without offering much supporting info); and whether we are going to make the responsible shooters' patrons (probably the Zetas or the Gulf kingpins) targets in the way that we pressured Mexico to go after the 1980s capos connected to the Camarena killing. In that regard, this quote from Janet Napolitano is open to interpretation:
Let me be clear: any act of violence against our ICE personnel…is an attack against all those who serve our nation and put their lives at risk for our safety. We remain committed in our broader support for Mexico's efforts to combat violence within its borders.