The family of Sergio Hernandez is seeking to sue the border official for their son's death. They say the agent violated Hernandez's constitutional rights.
The violent shooting was caught on cell phone video and sparked outrage because fact that Hernandez was unarmed.
This is the first case the Supreme Court heard under the new administration and comes as President Donald Trump's policies concerning his executive order on immigration have raised questions about the constitutional rights of non-citizens. Another backdrop is the tense relations between the Trump administration and Mexico over the issue of building a wall between the two countries.
In court the justices peppered attorneys on both sides. Some on the court seemed to be concerned with a limiting principle. For instance this case involves a Mexican national on Mexican soil. If the court were to rule that the case should go forward, that Hernandez as a non citizen on Mexican soil had enough connection to the US, could such an opinion open up similar claims in cases abroad concerning drone strikes on foreign soil.
Justice Anthony Kennedy, who could be a key vote, expressed concern at one point that this matter is in a "sensitive area" and he wondered whether it could it be better handled not by the courts, but the political branches.
The court also has now gone more than a year with only eight justices, following the death of Justice Antonin Scalia. Trump's nominee, Judge Neil Gorsuch, is set for Senate hearings next month.
The the justices were to split 4-4, they'd be left simply upholding the lower court ruling that went in favor of the agent.
While the family says Hernandez was playing with his friends along the US/Mexcian border near El Paso, the government alleges that the shooting occurred while "smugglers" were attempting an illegal border crossing hurling rocks at close range at the agent, Jesus Mesa.
Among the issues before the court is whether the case can be brought, or whether the officer is entitled to qualified immunity for the shooting. The court may also consider whether the Fourth Amendment's guarantee against unreasonable search and seizure applies to Hernandez.
While the government is siding with the agent, Mexico has signed a brief in support of Hernandez.
Lawyers for the Hernandez family lost their bid in a lower court when it concluded that the Constitution did not offer Hernandez any protection in part because he had no significant voluntary connection to the United States.
"If left standing, the Fifth Circuit's decision will create a unique no-man's land -- a law-free zone in which US agents can kill innocent civilians with impunity," Robert Hilliard, a lawyer for Hernandez, argued in court papers. "This court should make clear that our border is not an on/off switch for the Constitution's most fundamental protections."
The Trump administration says "judicial examination of the government's treatment of aliens outside the US would inject the courts into sensitive matters of international diplomacy."
Mexico has filed a brief in support of Hernandez referencing US Customs and Border Protection statistics citing the deadly use of force involving firearms 243 times from October 2010 through August 2016, nearly all of them at or near the US-Mexico border.
"When agents of the United States government violate fundamental rights of Mexican nationals and others within Mexico's jurisdiction, it is a priority to Mexico to see that the United States has provided adequate means to hold the agents accountable and to compensate the victims," wrote Donald Francis Donovan, an attorney for the government of Mexico.