It's curious, though, that Congressional investigators did not respond to Univision's request for serial numbers (per the ABC report). You would think they would respond in some manner, even if only to explain why they could not turn over the numbers. Instead, Univision had to compare using some deductive reasoning.
While the murder of a U.S. Border Agent with one of the weapons might conceivably have been unforeseeable, the use of guns to commit murder and other crimes in Mexico was almost inevitable. Obama apologizes for everything else. I can't see why he won't apologize to Mexico and the families of the victims. Oh, wait --- I do know why. It happened on his watch, not somebody else's.