Mexican prosecutors announced that they had opened a murder investigation in the death of a Mexican man shot by US officials while trying to sneak into California.
The federal Attorney General's Office said in a statement on Monday that the probe was opened against "whoever is found to have been responsible," but did not name an actual suspect. Mexico generally does not try to apply its laws to events that occurred in other nations.
Guillermo Martinez, 18, died on Saturday in a Tijuana hospital, the Baja California state attorney general's office said. He died one day after he was shot by a US Border Patrol agent near a metal wall separating that city from San Diego, according to witnesses cited by Mexican officials.
"An agent was assaulted by an individual who threw a large size rock," Raul Martinez, a spokesman for the US Border Patrol in San Diego, said on Monday.
"The agent, fearing for his life at that time, fired one round at the individual, who fled back to Mexico," he said.
Raul Martinez, who is not related to the victim, said the shooting occurred in US territory, about 46m north of the primary fence and 1km east of the San Ysidro border crossing.
He said San Diego police were investigating the incident. He said he could not release the name of the agent involved until the case is closed.
Mexican President Vicente Fox said the death showed that extending border walls will not curb illegal immigration. He said US investigators were unsure if the victim had been struck by the bullet because he crossed back into Mexican territory.
The press statement from Mexico's Attorney General said Guillermo Martinez was in the company of four other people when he was shot.
At his briefing with reporters in Mexico City, Fox's chief spokesman, Ruben Aguilar, said the government "laments and condemns" Martinez's death.
"This occurrence does no more than provide evidence that only a law that guarantees legal entry and is respectful of human rights can resolve the migratory problem both countries face," Aguilar said.
Martinez was from the western city of Guadalajara but was living in Tijuana with his older brother, who apparently witnessed the shooting, said Luis Cabrera, Mexico's consul general in San Diego. Cabrera said Mexican officials were collecting reports from him and other witnesses.
Many Mexicans were already angry about a bill passed by the US House of Representatives on Dec. 16 that would build more border fences, make illegal entry a felony and enlist military and local police to help stop undocumented migrants. The US Senate is expected to address the matter next month.
Mexico has bitterly opposed the House bill, which Foreign Relations Secretary Luis Ernesto Derbez branded as "stupid and underhanded." Fox has called it shameful.