Updated

The former head of internal affairs at U.S. Customs and Border Protection says in a Supreme Court filing that an agent who killed a Mexican teen in a cross-border shooting should be held accountable.

James Tomsheck said in a brief submitted Friday that poor screening and inadequate training has resulted in an environment in which Border Patrol agents use unnecessary lethal force on the U.S.-Mexico border.

Tomsheck was the assistant commissioner of the CBP Office of Internal Affairs from June 2006 to June 2014, overseeing use-of-force investigations.

The brief was filed in the Supreme Court case involving an agent who fatally shot 15-year-old Sergio Adrian Hernandez Guereca in 2010. A lower court ruled that the boy's family couldn't sue because he was in Mexico at the time of the shooting and wasn't constitutionally protected.