Washington (CNN) -- A U.S. investigation into the controversial fatal shooting of a 15-year-old Mexican boy by a U.S. Border Patrol agent has been closed without prosecution because of "insufficient evidence to pursue federal criminal charges," the Justice Department announced Friday.
The decision was immediately denounced by the Mexican Ministry of Foreign Affairs.
Mexico said it "deeply regrets and strongly rejects the decision by the Department of Justice." The Mexican Embassy said it was sending a note of protest to the U.S. government to underscore its concern.
The incident on the border in June 2010 had prompted criticism by the parents of Sergio Hernandez-Guereca. The family and supporters filed suit against the U.S. government, but the complaint was thrown out by a U.S. judge in August.
The court, however, allowed the family to pursue possible charges against the agent, Jesus Mesa Jr.
In its decision announced Friday, the Justice Department and the U.S. attorney for western Texas said their investigation showed that Hernandez and others threw rocks at close range at the agent, who was attempting to detain a suspect in a human-smuggling operation at the border.
The Civil Rights Division said there was no evidence that the agent had "deliberate and specific intent" to deprive Hernandez of his civil rights.
Officials said they had reviewed both "civilian and surveillance" video in their investigation but did not comment other than to say the evidence was not sufficient to prove beyond a reasonable doubt that the agent violated federal homicide laws.
At the time of the shooting, the Mexican government said it appeared to be an excessive response to the rock throwing. On Friday, Mexico said efforts against Mesa will continue in U.S. civil courts and in Mexican courts.
Hernandez's parents said he was a straight-A student, but U.S. authorities described him as a repeat juvenile offender who had a history of ties to human smuggling.