IOW, bring me the witch's broom before I answer questions, says the almighty wizard of dirtboy.
Second, DHS seems to be saying that it was compelled to disclose whatever information it may have given to Mexico by the 1963 Vienna Convention on Consular Relations, which President Nixon ratified in 1969.
This latter claim bears scrutiny. The consular-notification convention, and in particular its Article 36, comes into play whenever an alien—legal or illegal—is arrested in the United States. It absolutely does not require U.S. authorities to provide any investigative information or other intelligence to foreign governments. Indeed, it does not necessarily require our government to give a foreign government any information whatsoever. On the contrary, it provides that when a foreign national is detained, he has a right to have his nation’s consulate in the United States informed of the fact of the arrest. If he does not want his nation so advised, the U.S. is under no obligation to provide notice.
If the detainee does assert his consular-notification rights, the U.S. must advise the consulate of the fact of the arrest, pass along any communications the detainee addresses to his consulate, and allow representatives of the consulate to visit with the detainee.
That’s it. If the foreign government is determined to educate itself about the case, it must do so by interviewing the arrestee (just like a defense lawyer) or by open source information (just like a reporter or any person curious enough to check the public record). It has no claim on investigative or intelligence information maintained by the United States government. Of course, our government may decide to share more information with the foreign government; but if it does, that is a function of choice, not a requirement of law.