|The US government said Texas authorities did not inform Garcia of his right to have access to Mexican consular officials
The Obama administration has called on Texas to delay the execution of Humberto Leal Garcia until the end of this year because he was not told at the appropriate time of his rights to diplomatic counsel.
Leal Garcia, 38, was convicted of raping a 16-year-old girl and then killing her with a piece of asphalt in Texas in 1995.
He is scheduled to be executed by lethal injection on Thursday.
The US state department said the US government had determined that when arrested, Texas authorities did not inform Leal Garcia of his right to have access to Mexican consular officials, as they are required to under the Vienna Convention on Consular Relations.
"This is an issue of reciprocity for the United States. It is critical for our ability to get consular access and protection for our own citizens when they find themselves in similar circumstances when they are arrested or detained by foreign governments," Victoria Nuland, the state department spokesperson, said.
Alberto Rodriguez, Leal Garcia's uncle, who lives in Monterrey in Nuevo Leon state, said his nephew knew who the real killer was and that he knew of witnesses.
"He has witnesses who saw the real killer, who is walking free. He also lives in San Antonio but he's American," he said on Monday as he showed photographs of his nephew at a wedding.
Rodriguez added that Leal Garcia had been stripped of his US citizenship upon his sentencing.
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"For the moment of his sentence, he was stripped of his papers, they destroyed them. He is another Mexican over there who is paying for something he did not do. We'll wait for him here with open arms," he said.
Leal Garcia's relatives held banners that read "Mexican government, please help" as they asked for a meeting with Rodrigo Medina, Nuevo Leon state governor, which they obtained.
The Texas board of pardons and paroles on Tuesday denied Leal Garcia's request for a reprieve or commutation of his sentence, leaving any final decision on his fate to either the Supreme Court or Rick Perry, the Texas governor.
Silvia Vazquez, a lawyer from the Mexican commission for the defence and promotion of human rights, said they were doing everything they could to halt the execution.
"We have to review the areas where the procedure was violated. If we can present something to help prove his innocence, witnesses, evidence, whatever, that could help his situation to change his sentence," Vazquez said.
A spokesperson for Perry told the Reuters news agency that the governor had no plans to halt the execution and that the Texas attorney general's office had urged the Supreme Court not to intervene.
"Perry has a special affection for the death penalty, so I think he will be executed," Ricardo Mendez Silva, an international law expert told Al Jazeera.
The Obama administration urged the Supreme Court to delay the execution until the end of this year so Congress could pass legislation that would give Leal Garcia and other foreign nationals the right to federal review of his claim that he was not given the option of consular access.
The administration said that allowing his execution to go forward could have serious repercussions on US
foreign relations and implications for US citizens arrested abroad.