The office said in a statement yesterday that Andrew Tahmooressi was arrested on weapon charges because he was carrying a pistol, shotgun and rifle and ammunition when he crossed into Tijuana.
"In Mexico, like in the United States, ignorance of the law, error, misperceptions or misunderstandings about the consequences of violating a law, are not exemptions from responsibility," prosecutors said.
The possession of any weapon restricted for the use of the Army is a federal crime in Mexico regardless of whether visitors declare it or not upon entering the country.
He has said he never intended to leave the United States but missed an exit.
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Prosecutors said the 25-year-old Afghanistan war veteran was placed in the clinic of a Tijuana prison after he acted aggressively, tried to escape twice and hurt himself physically. He's now being held at a prison in the border city of Tecate.
The office said Tahmooressi's rights have been respected and he has been visited more than 50 times by his lawyers, relatives, pastor and US Congressman Matt Salmon.
The office said Tahmooressi decided to hire a new defence lawyer and that's why the hearings in his case have been postponed. New dates haven't been set.
There have been similar cases in the past. In 2008, an active-duty Army soldier was jailed in Ciudad Juarez, across from El Paso, Texas, for driving into Mexico with guns, knives and ammunition. Former Army Spc. Richard R. Medina Torres also said he was lost and missed the last US exit. He spent a little over a month in jail before being released.