The 38-year-old Mexican citizen was executed by lethal injection for raping and bludgeoning Adria Sauceda, 16, to death with a 40-pound chunk of asphalt.
U.N. High Commissioner for Human Rights Navi Pillay said Leal's execution 'raises particular legal concerns', including whether he had access to consular services and a fair trial.
Pillay also cited a 2004 International Court of Justice ruling saying the U.S. must review and reconsider the cases of 51 Mexican nationals sentenced to death, including Leal's.
He claims this never happened.
In his last statement before he died, Leal apologized to the victim's family and asked for their forgiveness, according to MSNBC.
He said: 'I truly am sorry. That is all. Let's get this show on the road.
'One more thing: Viva Mexico, Viva Mexico'
Texas executed Leal despite objections from President Obama's administration that the action would violate international treaty obligations and put U.S. citizens abroad at risk.
The high court's 5-4 decision was a setback for the administration. Read More