WASHINGTON (AP) — The Supreme Court is taking up an appeal from the parents of a Mexican teenager who was killed by a U.S. Border Patrol agent. The case could help define when foreigners outside the U.S. have access to American courts.

The justices are hearing argument Tuesday in a case that arose from a June 2010 incident in the cement culvert that separates El Paso, Texas, from Ciudad Juarez, Mexico.

Exactly what occurred is in dispute, but it's clear that the agent was on the U.S. side of the border when he fired his gun, striking the teenager on the Mexican side.

Lower courts dismissed the parents' lawsuit. The Supreme Court is considering whether noncitizens who are injured or killed outside the country can have their day in American courts.