Gunmen raid trains, demanding money and taking prisoners. Government officials run human trafficking rings. Police find the bloodied bodies of slain immigrants on an abandoned ranch.
Allegations from authorities paint a bleak picture of life for thousands of Central Americans heading to the United States through Mexico.
The discovery and detention of more than 500 illegal immigrants crammed into two semi-trucks in southern Mexico this week was a startling reminder of the desperation that drives many -- and the dangers they face.
"They are very vulnerable. They face risks of all kinds," said Diana Martinez, a lawyer with Sin Fronteras (Without Borders), a Mexican immigrant rights organization.
Experts say many Central American migrants passing through Mexico on their way to the United States are victims of violence along the Mexico-U.S. border, but the journey is perilous from the moment it begins. And the danger is growing as Mexico's drug gangs expand their reach.