Updated

The U.S. Supreme Court on Thursday was considering whether to block a Mexican citizen's execution for the rape and murder of a teenager in a case where Texas justice clashed with international treaty rights. The White House was among those pleading for a stay, saying the case could affect not only foreigners in the U.S. but Americans detained in other countries.

The Obama administration asked the high court to delay Humberto Leal's execution, set for Thursday evening, so Congress could consider a law that would require court reviews in cases where condemned foreign nationals did not receive help from their consulates. Prosecutors say such legislation is likely to fail, and that Leal's appeals are simply an attempt to evade justice for a gruesome murder.

Leal, a 38-year-old mechanic, was sentenced to lethal injection for the 1994 rape-slaying of 16-year-old Adria Sauceda, whose brutalized nude body was found hours after Leal left a San Antonio street party with her. The girl's head was bashed with a 30- to 40-pound chunk of asphalt.

Leal moved with his family from Monterrey, Mexico, to the U.S. as a toddler. His appeals contended police never told him he could seek legal assistance from the Mexican government under an international treaty, and that such assistance would have helped his defense.

The argument is not new. Texas, the nation's most active death penalty state, 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.

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 legislation would give Mr. Leal an opportunity to demonstrate that with consular assistance, he likely would not have been convicted, let alone sentenced to death," said Sandra Babcock, a Northwestern University law professor and one of Leal's lawyers.

The Mexican government and other diplomats also contend 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 abroad.

Measures similar to Leahy's have failed at least twice in recent 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."

Stephen Hoffman, an assistant attorney general, also 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.

There was evidence Sauceda had been bitten, strangled and raped. A large stick that had a screw protruding from it was left in her body.

A witness testified that Leal's brother appeared at the party, agitated that Leal had arrived home bloody and saying he had killed a girl.

In his first statement to police, Leal said Sauceda bolted from his car and ran off. After he was told his brother had given detectives a statement, he changed his story, saying Sauceda attacked him and fell to the ground after he fought back. He said when he couldn't wake her and saw bubbles in her nose, he got scared and went home.

Testifying during his trial's punishment phase, Leal acknowledged being intoxicated and doing wrong but said he wasn't responsible for what prosecutors alleged. A psychiatrist testified Leal suffered from alcohol dependence and pathological intoxication.

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.

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, negating the decision.