Joel Luna seemed an ideal Border Patrol hire: south Texas native, high school ROTC standout, Army combat veteran.

Luna worked out of a border checkpoint about 100 miles north of Mexico in Hebbronville, patrolling ranch land frequented by smugglers of humans and drugs. The covert work drew upon his infantry experience.

But now Luna, 31, is preparing to stand trial on a charge of capital murder for his role in what prosecutors say was a cartel drug trafficking conspiracy that left a decapitated corpse floating off the Texas coast during spring break.

To hear prosecutors tell it, the conspiracy is a tale of three Lunas — brothers Joel, Fernando and Eduardo.