Since this was an international crime, couldn't Interpol be pulled in? Interesting premise if it could work.
An interesting question. However, while this certainly appears to be violations of both U.S. and Mexican laws, it's far from clear to me that international law was broken. Mind you, I'm no attorney, much less an attorney versed in international law, but best I can tell no international laws (such as they are) or treaties appear to have been violated.
Moreover, isn't Interpol primarily involved when the subject of an investigation is not found within the jurisdiction in which the crime occurred? That wouldn't seem to be in play here.