Texas executes Mexican national over protests from Mexico and John Kerry

From Thomas Lifson at American Thinker:

Edgar Tamayo, 46, met his maker last night, executed by lethal injection for the cold-blooded murder of a Houston police officer. The government of Mexico strongly protested the execution because Tamayo had not been informed of his right to receive consular assistance in a timely fashion, under provisions of 1963 Vienna Convention on Consular Relations. Secretary of State John Kerry joined in the protest, warning that it ""could impact the way American citizens are treated in other countries." But the United States Supreme Court did not agree and permitted the death sentence to be carried out.

The following is a description of how Tamayo killed the officer.

[Officer Guy] Gaddis, who had been on the force for two years, was driving Tamayo and another man from a robbery scene when evidence showed the officer was shot three times in the head and neck with a pistol Tamayo had concealed in his pants. The car crashed, and Tamayo fled on foot but was captured a few blocks away, still in handcuffs, carrying the robbery victim's watch and wearing the victim's necklace.

So, how would contacting the Mexican Consulate have made a difference?

Would it have made a difference?

One last note, the Associated Presses' news article only mentions Tamayo's illegal immigration status toward the end of it's article. I wonder why?