Texas officials pressed ahead Wednesday with plans to execute a Mexican man who killed a police officer but was not told he could meet with consular officials from Mexico after his arrest, as required by an international treaty.

"It doesn't matter where you are from, if you commit a despicable crime like this in Texas, you are subject to our state laws, including a fair trial by jury and the ultimate penalty," said Lucy Neshed, a spokeswoman for Texas Gov. Rick Perry's office.

Attorneys for Edgar Tamayo filed last-hope appeals to stop his execution scheduled for after 6 p.m. local time for the 1994 murder of Guy P. Gaddis.

Tamayo shot Gaddis, a Houston police officer who had arrested Tamayo for robbery. Tamayo was handcuffed in the patrol car, pulled a gun and shot the officer in the back of the head several times.

Mexican national Edgar TamayoTexas Department of Criminal Justice via AP

Attorneys have argued that without the chance to meet with Mexican consular officials, Tamayo, 46, was not assessed for mental retardation and received no language help. He spoke limited English then.

The attorneys have accused Perry and Attorney General Greg Abbott of breaking a promise to review cases of foreign nationals who were not informed of their rights afforded under the Vienna Convention on Consular Relations.

"It is dismaying that Texas' highest officials think so little of keeping their word," said Maurie Levin, one of Tamayo's attorneys.

Secretary of State John Kerry had asked the state to reconsider, raising concerns about how it would affect Americans abroad also protected by the treaty.

The U.S. Supreme Court said in 2008 the international treaty is not binding on states.