The confessed ringleader in a 2003 smuggling operation that left 19 illegal immigrants dead has refused to testify for the defense in former trucker Tyrone Williams' trial in Houston.

According to The Associated Press, Carla Chavez Hoya fears her testimony could hurt her own defense. She was previously sentenced to 17 years in prison for her role - but prosecutors are appealing that sentence, saying she deserves life in prison.

Williams drove the truck in which the immigrants died, mostly from heat and suffocation.