A fourth suspect in the nation's deadliest human smuggling event has pled guilty in a San Antonio federal court. Luis Rivera-Leal was part of the group that moved an 18-wheeler full of illegal immigrants from the border to San Antonio in 2022. Forty-seven adults and six children died in the trailer in the sweltering June heat. Rivera-Leal, whose nickname is "Cowboy," is a Mexican national. His guilty plea to a single count of conspiracy to transport aliens carries a maximum sentence of 20-years in prison. Cases are still pending for three others, including the driver of the big rig.