Family members of Mexico's missing students give their DNA, hoping that will help federal investigators to find their loved ones.
Forty-three teachers in training disappeared in Guerrero in September, after clashing with local police.
Some of their relatives say they don't trust the state authorities and are scared of being targeted themselves.
(SOUNDBITE) (Spanish) RELATIVE OF MISSING STUDENT, ESPERANZA MELENDEZ, SAYING:
"It's always about fear, fear because if you speak out against something the authorities pay no attention to what you're speaking out against. Now, however, they're investigating us to see where we work, if we're involved in bad things. They're trying to cling onto something and don't pay any attention."
Investigators suspect the students were killed by corrupt officers working with drug gang members.
The case has sparked a few violent protests. Many say the government isn't doing enough to stop endemic gang violence that's killed t