In his last minutes, Humberto Leal repeatedly said he was sorry and accepted responsibility.
"I have hurt a lot of people. ... I take full blame for everything. I am sorry for what I did," he said in the death chamber.
"One more thing," he said as the drugs began taking effect. Then he shouted twice, "Viva Mexico!"
"Ready warden," he said. "Let's get this show on the road."
The 38-year-old mechanic was pronounced dead 10 minutes after the lethal drugs began flowing into his arms.
He was sentenced to death for the 1994 murder of 16-year-old Adria Sauceda, whose brutalized nude body was found hours after he left a San Antonio street party with her. She was bludgeoned with a chunk of asphalt.
Leal was just a toddler when he and his family moved to the U.S. from Monterrey, Mexico, but his citizenship became a key element of his attorneys' efforts to win a stay. They said police never told him following his arrest that he could seek legal assistance from the Mexican government under an international treaty.
Mexico, the Obama administration and others had asked the U.S. Supreme Court to delay Leal's execution so Congress could consider a law that would require court reviews in cases where condemned foreign nationals did not receive help from their consulates. They said the case could affect not only foreigners in the U.S. but Americans detained in other countries.
The court rejected the request 5-4. Its five more conservative justices doubted that executing Leal would cause grave international consequences, and doubted "that it is ever appropriate to stay a lower court judgment in light of unenacted legislation."
"Our task is to rule on what the law is, not what it might eventually be," the majority said.
The court's four liberal-leaning justices said they would have granted the stay.
Leal's attorney Sandra L. Babcock said that with consular help her client could have shown that he was not guilty. But she added, "This case was not just about one Mexican national on death row in Texas. The execution of Mr. Leal violates the United States' treaty commitments, threatens the nation's foreign policy interests, and undermines the safety of all Americans abroad."
Prosecutors, however, said Congress was unlikely to pass the legislation sought and that Leal's appeals were simply an attempt to evade justice for a gruesome murder.
Mexico's foreign ministry said in a statement that the government condemned Leal's execution and sent a note of protest to the U.S. State Department. The ministry also said Mexican ambassador Arturo Sarukhan attempted to contact Texas Gov. Rick Perry, who refused to speak on the phone.
The governor's office declined to comment on the execution Thursday.
Leal's argument that he should have received consular legal aid that could have helped his case was not new. Texas has executed other condemned foreign nationals who raised similar challenges, most recently in 2008.
Leal's appeals, however, focused on legislation introduced last month in the U.S. Senate by Vermont Democrat Patrick Leahy. Leahy's measure would bring the U.S. into compliance with the Vienna Convention on Consular Relations provision regarding the arrests of foreign nationals, and ensure court reviews for condemned foreigners to determine if a lack of consular help made a significant difference in the outcome of their cases.
"Americans detained overseas rely on their access to U.S. consulates every day," Leahy said after the Supreme Court decision was announced. "If we expect other countries to abide by the treaties they join, the United States must also honor its obligations."
The Obama administration took the unusual step of intervening in a state murder case last week when Solicitor General Donald Verrilli Jr. joined Leal's appeal, asking the high court to halt the execution and give Congress at least six months to consider Leahy's bill.
The Mexican government and other diplomats also contended that the execution should be delayed so Leal's case could be thoroughly reviewed. Some also warned his execution would violate the treaty provision and could endanger Americans in countries that deny them consular help.
Measures similar to Leahy's have failed at least twice in recent U.S. congressional sessions. The Texas Attorney General's office, opposing the appeals, pointed to those failures in its Supreme Court arguments and said "legislative relief was not likely to be forthcoming."
After his execution, relatives of Leal who had gathered in Guadalupe, Mexico, burned a T-shirt with an image of the American flag in protest. Leal's uncle Alberto Leal criticized the U.S. justice system and the Mexican government and said, "There is a God who makes us all pay."
In 2005, President George W. Bush agreed with an International Court of Justice ruling that Leal and 50 other Mexican-born inmates nationwide should be entitled to new hearings in U.S. courts to determine if their consular rights were violated. The Supreme Court later overruled Bush.
Stephen Hoffman, an assistant Texas attorney general, said evidence pointing to Leal's guilt is strong.
"At this point, it is clear that Leal is attempting to avoid execution by overwhelming the state and the courts with as many meritless lawsuits and motions as humanly possible," Hoffman said.
Prosecutors said Sauceda was drunk and high on cocaine the night she was killed, and that Leal offered to take her home. Witnesses said Leal drove off with her around 5 a.m. Some partygoers found her brutalized nude body later that morning and called police.
Sauceda's mother, Rachel Terry, told San Antonio television station KSAT her family already had suffered too long.
"A technicality doesn't give anyone a right to come to this country and rape, torture and murder anyone," she said.
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Associated Press Writer Jesse J. Holland in Washington contributed to this report.
