The United States Supreme Court is due to decide whether to issue a stay of execution, which Texas state lawyers insist should go ahead.
If the Supreme Court does not intervene, Leal's fate will lie in the hands of Governor Rick Perry of Texas, who is currently pondering whether to join the 2012 presidential race.
Texas executes more prisoners than any other US state. In his 10 years in office Mr Perry has refused clemency in 230 executions, almost half the 470 executions in Texas since the death penalty was reinstated in 1974.
Among other evidence against Leal, a bite mark was matched to him and the victim's bloody blouse was found at his home. Leal told police that she had attacked him and had fallen and lost consciousness.
Even Leal's lawyers concede that it was "plausible" he was responsible for Miss Sauceda's death. But they contend that if he had been given consular assistance rather than a state-appointed defence lawyer he would probably have been convicted of manslaughter.
The Obama administration, adopting a similar stance to the one taken by President George W Bush's, believes executing Leal could endanger Americans abroad who are also entitled to consular assistance under the Vienna Convention.
"This case implicates United States foreign-policy interests of the highest order," said Donald Verrilli, Mr Obama's Solicitor General in an amicus brief filed in the Supreme Court case.
"The imminent execution of petitioner would place the United States in irreparable breach of its international law obligation."
Executing him, he said, "would have serious repercussions for United States foreign relations, law enforcement and other co-operation with Mexico, and the ability of American citizens travelling abroad to have the benefits of consular assistance in the event of detention".
There is legislation pending in the US Senate would allow federal courts to review cases of condemned foreign nationals to determine whether the lack of consular help made a significant difference in the outcome of their cases.
The United Nations, Amnesty International and a number of former diplomats and military officers have requested that the sentence be commuted to life.
Mr Perry has commuted the death sentences of 31 inmates. Of these, 28 involved cases in which the defendant was a juvenile at the time of the crime and Mr Perry acted after a Supreme Court ruling on the issue.
Polls show that about 65 per cent of Americans favour the death penalty. Mr Perry's enthusiastic backing for the death penalty would be unlikely to be an issue that could harm him in the Republican primaries. It could, however, became an issue in a general election against Mr Obama, who supports the death penalty but is much more willing to consider exclusions.