Local congressmen are getting involved in a case of a Marine Corps veteran imprisoned in a Tijuana.

SAN DIEGO -- A bipartisan group of 21 members of Congress has appealed to the Mexican government to free a Marine veteran of Afghanistan who is being held on weapons charges in a prison in Tijuana.

Andrew Tahmooressi, 25, now in the Marine reserves, has been held in the La Mesa prison since April 1 after he was charged with being an arms trafficker.

Tahmooressi insists that he mistakenly drove across the border at San Ysidro in a truck stuffed with all of his possessions, including a handgun, rifle and shotgun.

Led by Reps. Duncan Hunter (R-Alpine) and Juan Vargas (D-San Diego), the 21 members of Congress sent a letter to the Mexican government through its embassy in Washington. A separate letter was sent by Rep. Scott Peters (D-San Diego) to Secretary of State John Kerry.

"We fully respect Mexico's right to enforce its laws, but we believe Andrew is not a criminal or a weapons trafficker," said the letter signed by Hunter, Vargas and the others. "He is a Marine Corps veteran who served his country honorably, and simply got lost in an area that he was unfamiliar with."

The members of Congress hope that the Mexican attorney general will use his authority to drop the charges.

Tahmooressi had recently moved to San Diego from his home in Florida. He has said he was looking to meet with friends in San Ysidro but got confused in the lanes leading to the border crossing and missed the turnoff to remain in the U.S.

While in the La Mesa prison, Tahmooressi attempted to escape but gave up when a guard fired a warning shot. There is no indication that Mexican authorities plan to add an escape charge.

Tahmooressi served with the Camp Lejeune, N.C.-based 2nd Battalion, 6th Regiment, and was meritoriously promoted to sergeant. He is now in the Individual Ready Reserves.

He had moved to San Diego in hopes of receiving treatment for post-traumatic stress disorder at the Veterans Affairs hospital in La Jolla.

"I urge that everything possible be done to ensure his safety, well-being, fair treatment and quick return," Peters wrote to Kerry.