Previously, illegal immigrants tramped across the course and into the hands of Border Patrol agents, knowing they wouldn't face jail.
With the experiment, U.S. officials prosecuted and imprisoned the immigrants before returning them home as criminal convicts under a "zero tolerance" policy.
Border arrests are at a 40-year low, and immigrant hawks say they want the policy extended to the entire U.S.-Mexico frontier. Some experts, though, say the slow U.S. economy is a big factor in the drop, and top Obama administration say the policy is just one part of its new border enforcement strategy.
