The US state of Texas has executed Humberto Leal Garcia, 38, a Mexican national, despite an unusual appeal by President Barack Obama.
The US supreme court rejected a last-minute stay of execution in the case, in which Leal Garcia was not informed of his rights in violation of US law at the time of his arrest.
Leal Garcia was convicted of raping a 16-year-old girl and then bludgeoning her to death in 1994 in Texas.
He was executed by lethal injection at 23:00 GMT on Thursday in Huntsville, Texas.
Obama's appeal was premised on concerns that police misconduct in the case amounted to an international treaty violation.
"There are around 50 similar cases, all Mexican citizens, who are on death row waiting to be executed and the president basically said they did not get consular attention and that puts our citizens [US] at risk," Al Jazeera's Monica Villamizar, reporting from Mexico City, said.
The US state department said that the government 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.
The Mexican government and other diplomats also contended that the execution should be delayed so Leal Garcia's case could be thoroughly reviewed.
The Mexican foreign ministry office said that Rick Perry, the Texas governor, refused to return calls to Mexico's ambassador in the US, Arturo Sarukhan, who told Al Jazeera that he thinks "the United States is in violation of international law".
It was not clear whether officers who made the arrest in violation of US policy would receive any penalty.
'Long live Mexico'
Before he was executed, "Leal Garcia asked for forgiveness from the victim and the parents, who were not there ... in the execution chamber, although they had the choice", our correspondent said.
"And he said 'long live Mexico'. And he told the executioner 'let's get this show on the road'. Those were his last words."
Friends and relatives of Leal Garcia gathered in Mexico and burned a T-shirt with an image of the American flag in protest.
Leal's uncle, Alberto Leal, criticised the US legal system and the Mexican government for not stopping the execution.
In 2005, George Bush, the then US president, agreed with an International Court of Justice ruling that Leal and the 50 other Mexican-born inmates nationwide should be entitled to new hearings in US courts to determine if their consular rights were violated.
Bush, who gained notoriety for signing off on the executions of more prisoners than any other governor during his tenure as governor of Texas, was overruled by the US supreme court.