The Supreme Court on Tuesday, in a 5-4 ruling, closed the courthouse door on the parents of a Mexican teenager who was shot dead over the border by an American agent.

The court's five conservative justices ruled that the parents could not sue Border Patrol Agent Jesus Mesa Jr., who killed their unarmed 15-year-old son in 2010.

Justice Samuel Alito wrote for the court that the case is tragic, but that strong border security and international relations issues led to the ruling against the parents of Sergio Adrian Hernandez Guereca.

Justice Ruth Bader Ginsburg, writing for her liberal colleagues, disagreed, saying the parents' lawsuit does not endanger border security or U.S. foreign policy.

Mesa fired into Mexico, striking and killing Sergio, who was playing a game with friends on a June evening, running through a culvert and over the border, touching it, and running back. Mesa rode up on a bicycle, took Sergio's friend into custody, then fired across the border, killing Sergio with a gunshot wound to the face.