The U.S. Supreme Court on Tuesday appeared evenly divided on the right of Mexican parents to file a lawsuit in American courts against a U.S. border agent who killed their teenage son by firing a shot across the U.S.-Mexican border.

Justice Anthony Kennedy and other conservatives on the court voiced skepticism about the parents’ lawsuit, while the court’s four liberal justices indicated they supported it because the 2010 shooting occurred near the border in an area the two countries jointly maintain.

A 4-4 split among the justices would leave in place a lower-court ruling dismissing the claims brought by the parents against the agent, Jesus Mesa. However, the court could delay a ruling in the event of a tie vote and wait to see whether the Senate confirms the nomination of a conservative appellate court judge, Neil Gorsuch, to fill the open, ninth seat on the court. The Supreme Court could then hear new arguments in the dispute.

Kennedy said the Mexican and American governments should resolve the case, noting that the border “is one of the most sensitive areas in foreign affairs.”

The court case stems from an incident that occurred in a cement culvert that separates El Paso, Texas, from Ciudad Juarez, Mexico.

The circumstances of the shooting remain in dispute, but it is clear that Mesa was on the U.S. side of the border when he fired a shot, killing Sergio Hernandez on the Mexican side. The high court is weighing what rights foreigners have to file a lawsuit in the U.S. judicial system.

The border area remains at the forefront of U.S. immigration concerns, with President Donald Trump vowing to build a wall to thwart illegal immigration into the United States.

On Tuesday, the U.S. announced tougher rules aimed at deporting undocumented immigrants who have been charged with crimes or convicted, while adding thousands of new agents to patrol the border.