For the past 14 months, agents from the DEA, FBI and U.S. Customs Service who were to form the backbone of the U.S. portion of the force have refused to cross the border because they are not allowed to carry weapons in Mexico. And at least five senior Mexican officers involved in the program have been arrested on suspicion of taking money from drug traffickers, kidnapping key witnesses or stealing confiscated cocaine. The units, called Bilateral Border Task Forces, initially were established in Tijuana and Ciudad Juarez -- seats of the large ....