The Marines were put on the border in Texas to observe activity of suspected drug smuggling at a river border crossing. They had been given false information relating to the local townspeople, which said that 75% of then were involved in drug trafficking. None of the local landowners were aware of their presence. (The reality was - it was the Sheriff of the County that had been driving cocaine across the border in his horse trailer for years. He was finally busted with 3 tons).
Esequiel, a local high school student, went out to graze his family's goats, taking his .22 rifle to protect the herd from wild dogs and coyotes as he always did. The Marines came upon Esequiel (with his goats) and immediately suspected him of being a criminal. The Marines were heavily camouflaged and hiding. Esequiel saw movement in their direction and fired his gun. It's not known if he fired at the Marines or something else. The Marines assumed he had fired at them, but the kid could not have known it was Marines in camouflage.
The Marines were angry and excited, and the squad leader wanted to pursue the kid and "neutralize" him, though this went against their order to follow the "Rules of Engagement". They stalked him for some time closing the distance between them. Then one of the Marines shot and killed the boy.
The story that was told was that Ezequiel had raised his gun to fire at them a second time, which was a fabrication according to the FBI and Marine investigators and other law enforcement officers, as well as three of the Marines involved. The forensic evidence proved that the boy was not aiming his gun at them but facing the other direction.
Both the Department of Defense and the Justice Departmant blatantly lied about the incident, covering up the truth that a Marine murdered a good Texan.