I just spent awhile looking into this claim, that the police were supposed to inform him of his right to speak to the Mexican Embassy.
I think the defense is bluffing and misconstruing the facts.
It is true, that there are some countries on a mandatory list, and here are the requirements:
When foreign nationals from most countries are arrested or detained, they may, upon request, have their consular officers notified without delay of their arrest or detention, and may have their communications to their consular officers forwarded without delay. In addition, foreign nationals must be advised of this information without delay.
For foreign nationals of some countries, consular officers must be notified of the arrest or detention of a foreign national even if the foreign national does not request or want notification.
Consular officers are entitled to communicate with and to have access to their nationals in detention, and to provide consular assistance to them, including arranging for legal representation.
However Mexico is NOT on the mandatory list of notifications.
ALSO, here is a key point:
STEPS TO FOLLOW WHEN A FOREIGN NATIONAL IS ARRESTED OR DETAINED
1. DETERMINE THE FOREIGN NATIONAL’S COUNTRY OF NATIONALITY. IN THE ABSENCE OF OTHER INFORMATION,
ASSUME THIS IS THE COUNTRY ON WHOSE PASSPORT OR OTHER TRAVEL DOCUMENT THE FOREIGN NATIONAL IS TRAVELING.
But in this case,
the murder suspect was not traveling with a passport or a travel document. He was here illegally, and had phone ID.
So I am not sure that this notification process would kick in, given the circumstances. This is the regulations and legal streps to follow when arrested a foreign national for DUI or robbery, etc, and the officer checks his ID and he is visiting from another country.
But this suspect was here, hiding from his country and from our country. I don't think he wanted to be in contact with his embassy, given his legal status at the time.
https://travel.state.gov/content/dam/travel/CNAtrainingresources/CNA Manual 5th Edition_September 2018.pdf