The U.S. Supreme Court denied a stay of execution for Mexican national Edgar Tamayo on Wednesday, allowing Texas to put to death the convicted killer who is also at the center of a diplomatic dispute.
Texas has until midnight local time (0600 GMT) to execute Tamayo at its death chamber in Huntsville.
The Mexican government has called on Texas to halt the execution, saying it would be a violation of international law and U.S. Secretary of State John Kerry has asked Texas Governor Rick Perry to consider a stay.
Tamayo, 46, was convicted of shooting dead Houston police officer Guy Gaddis in 1994. Gaddis had arrested him on suspicion of robbery.
While handcuffed in the police car, Tamayo pulled a pistol that had gone unseen and shot Gaddis, 24, three times in the back of the head. Tamayo kicked open a window and ran away from the car but was arrested again a few blocks from the scene.
The Mexican government contends Tamayo was not informed of his right, enshrined in an international treaty known as the Vienna Convention on Consular Relations, to diplomatic assistance.
In 2004, the United Nations' International Court of Justice ordered the United States to reconsider the convictions of 51 Mexicans, including Tamayo, who had been sent to death row without being informed of their consular rights.
So far, two of that group have been executed. Tamayo, who was in the United States illegally at the time of his arrest, would be the third.
Hoping for a miracle
In a statement on Sunday, Mexico's foreign ministry said, "If Edgar Tamayo's execution were to go ahead without his trial being reviewed and his sentence reconsidered ... it would be a clear violation of the United States' international obligations."
Last month, Secretary of State Kerry urged Governor Perry, a foe of the Obama administration, to reconsider Tamayo's execution because it could make it more difficult for the United States to help Americans in legal trouble abroad.
On Wednesday, the State Department said it has been in communication with Texas throughout the process. Texas argues it is not bound by the International Court of Justice ruling.
"Mr. Tamayo was convicted of killing a police officer," State Department spokeswoman Marie Harf told a news briefing on Wednesday.
"It's not that we don't take that seriously. It's that we take seriously our obligations to uphold consular access for folks incarcerated here because we go all over the world and ask other countries to do the same thing and apply those same obligations when our folks are incarcerated overseas," she added.
The case has drawn attention from around the world. Tamayo said his family had received letters of support from at least 67 countries.
In Tamayo's native town of Miacatlan in central Mexico, relatives were hoping for a miracle.
Some huddled next to radios anxiously listening for news from the United States, sipping on fermented pineapple juice.
"USA-Texas. Pardon Edgar Tamayo ... He is innocent," reads a banner on a major street through town.
"He was like any other guy, a bit crazy yes, feisty, but not to the point of killing someone," said his cousin Kenia, a housewife, declining to give her surname.
A U.S. federal judge in Austin, Texas, on Tuesday rejected a request to delay the execution brought on Tamayo's behalf, saying Texas was operating within its rights.
"The court concluded that the (parole) board's procedures provided Tamayo adequate due process in conformance with current Supreme Court precedent," U.S. District Judge Lee Yeakel wrote in a three-page opinion.
If the execution goes ahead, Tamayo would be the fourth person put to death in the United States this year and the first in Texas.
Texas has executed 508 prisoners since the reinstatement of capital punishment by the U.S. Supreme Court in 1976, the most of any U.S. state.
(Additional reporting by Liz Diaz in Miacatlan, Sandra Maler in Washington, Gabriel Stargardter and Julia Symmes Cobb in Mexico City and Scott Markley; Editing by Eric Walsh and Lisa Shumaker)