>> reporter: tonight, a country . tonight, a country spiraling into violence. >> inside that cooler we're told there's a human head. >> mexico torn apart by corruption and drug cartels. tens of thousands of people disappearing. now the mothers on a mission. >> i wrote a promise to my son. i will never surrender. i will never give up. >> searching for their sons and daughters, transforming their anguish into a tireless pursuit for answers. taking the fight from the streets straight to the president. a special edition of "nightline," the disappeared will be right back.

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to make her surrender. i, i wrote a promise to my son, and it's one of the things i say. i will never surrender. i will never give up. >> reporter: lucy diaz is searching for her son luis who disappeared six years ago. [ speaking in spanish ] >> this is the way, you know, we search for the possibility of a grave, you know? because once we hit underground like usually a meter and a half, two meters deep, we smell this bar. and then if it comes out with, it smells like, well, like a dead body. >> reporter: this is a skill

you've developed now to be able to smell for a dead body. >> yeah, yeah. and sometimes not only the smell. once i was hammering this and the, and i started to hear like a rattle underneath, because it was like a, not exactly breaking the bone, but it was making a noise, because it was rubbing against the bone. and there was a body. >> reporter: you think it's possible that right here underneath our feet there's a mass grave? >> very likely. here in veracruz, it's extremely likely. >> reporter: the state of veracruz is known as mexico's grave yard, with more than 200 mass graves uncovered here. i'm sitting here, i'm watching you guys, mothers, do this work. but you have a bunch of cops standing around just watching u why aren't they doing this? isn't it the job of the police

to investigate crimes and find bodies? >> it is, it is. but this is mexico, don't forget. keep that in mind. all your questions could be answered with this is mexico. >> reporter: mexico is a country at war with self. violence has reached record levels this year. this has been the deadliest year in mexico in more than two decades. gun cartels waging open gun battles in the streets. >> at least three women and six children were killed during an ambush. >> reporter: tourist destinations degenerating into chaos. inside that cooler, we're told there is a human head. as a result of this carnage, there are now by conservative estimates at least 40,000 missing people in mexico. in the face of a government that is overwhelmed, underresourced and riddled with corruption. the task of searching often

falls to the most committed. thousands of mothers all over this country. lucy diaz was leading a comfortable life as a college professor and mother of three, married to a successful businessman. everything changed one night in june of 2013. >> i don't even know what happened to him. at this point, five and a half years, and i have no idea. of his whereabouts or what happened. i know that he was kidnapped. but so far that's all i know. >> reporter: at the time her 29-year-old son luis was working as a popular deejay in the city of veracruz. he was a staple at weddings and parties. >> he was so passionate about his music, and then something like this happen, i just wish i could give him, you know, my life. >> reporter: one night, lucy got a nervous call from her son's

girl friend saying she hadn't heard from him in a couple days many lucy called one of her son's employees who promised her that luis was simply busy at a gig. >> and then one day i said there's something wrong. he knows i get crazy when i cannot get in touch with him. the next day i waited all day. but then around 8:00, i knew. i knew for a fact that it was terribly wrong. something was terribly wrong. and that's the beginning of this trip to hell. that doesn't have an end. >> reporter: the police did talk to that employee who assured lucy her son was okay, and it turned out he was lying. >> he broke down and said no, somebody kidnapped him. i was in the office, and he was in his bedroom. and i saw them come in. >> reporter: lucy also says that same employee sold luis's phone after he was kidnapped.

>> is he in jail? no. frias free as a bird. >> reporter: he's just walking around. >> yeah. who's in jail? me. i'm in the worst jail there is. >> reporter: last year, a potentially huge break in the case. the police found luis' mot motorcycle and the individual riding the bike, hoping this could lead to answers, lucy followed up with authorities in veracruz. >> did you bring him in at least to interrogate him? and they said not yet. they're still haven't interrogated him. >> reporter: do you think it's laziness? >> no, i think it's corruption. >> reporter: corruption. >> yes, they don't really want to solve the problem. they don't want to find the person. >> reporter: just to be clear, was your son in any way connected to the drug trade or criminal underground? >> no, and i can say that. in almost six years of investigations, the only one that has been investigated all over is him.

they don't leave any privacy to the victim. >> reporter: unwilling to accept investigative inaction, lucy became a very public critic of local authorities, a risky move here in this deeply-corrupt country. lucy has undergone, she says, an inner transformation from depression to anger to finally something much larger. she has now organized hundreds of other mothers who are also desperately searching for their children here in veracruz. we find them raising money by telling tamales at a local carnival, a sorority of anguish. mothers united around a wrenching mission. [ speaking in spanish ]

>> reporter: the money they raise is used to chase down leads they gather from anonymous tipsters and then launch their search mission. rosa leah castro is one of lucy's staunchest allies.

[ speaking in spanish ] >> reporter: it would not be the first time these mothers have found remains. just ten miles from this dump, more than 300 bodies were exhumed at a mass grave. >> all the moms say, till my dying day. just like we're going to fight for our children. it's nothing going to stop us. >> reporter: this struggle has taken over lucy's life. she quit her job as a professor and now balances her time between working on behalf of all of the mothers and doggedly pursuing her son's case. we take lucy's case to carla

quinna, the recently appointed national commissioner in charge of searching for the disappeared. >> this number of 40,000 people, they tell me the official number we have. >> reporter: so it could be double or triple that? >> that would be my guess. we know lots of disappearances are not taken to authorities. they're afraid of the same thor the authorities in some case. or the cartels. >> reporter: she is surprisingly blunt for a government official. how have we gotten to the point in this country where it's mothers who have to bear the injury of losing their children and then the insult of going to do the searches themselves? >> i think it's because the government, they don't care much about who has been disappeared. there is this stigma in mexico, that we all have to fight that if someone is disappeared it's because they were doing

something or they were involved in something, which is not true. >> reporter: we've been following the case of lucy diaz, and she's perhaps the most prominent mom involved in the searches. and it appears that there are very clear leads in this case that are just not being followed. and i wonder if somebody like lucy can't get the police to do anything, how can anybody expect any action on their case? >> mexican justice system is very poor. specifically regarding to people that are disappeared. we only have 30 decisions, judicial decisions in mexico. >> reporter: so sentencing somebody for making somebody else disappear, that's only happened 30 times? >> yeah. >> reporter: so essentially, in this country you can kill somebody, bury them in a shallow grave and get away it. >> well, i'm a public servant, but i would have to say yes.

>> reporter: with the official in charge of searching for the missing failing to provide much hope we decide to go all the way to the top, to the pred sident mexico. would you commit here and now to taking a look at her case to see if you can move it forward? when we come back. my moderate to severe crohn's disease. then i realized something was missing... me. my symptoms were keeping me from being there. so, i talked to my doctor and learned humira is for people who still have symptoms of crohn's disease after trying other medications. and the majority of people on humira saw significant symptom relief and many achieved remission in as little as 4 weeks. humira can lower your ability to fight infections, including tuberculosis. serious, sometimes fatal infections and cancers, including lymphoma, have happened; as have blood, liver, and nervous system problems, serious allergic reactions, and new or worsening heart failure. before treatment, get tested for tb. tell your doctor if you've been to areas where certain fungal infections are common,

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>> reporter: we've traveled to the state of guerrero, hundreds of miles from veracruz where lucy diaz lives. here we find another group of mothers joining a morbid

national movement. the families have set up a line here, and if they see something, they call people over to look. she is looking for her son s cesar. she says he just vanished one day like the earth all we all e whole. when you come out here, do you hope you will find your son or do you fear you will find your son? [ speaking in spanish ] >> reporter: you feel like you're near him? this multiple-day search yields results. could these remains be one of these mothers' missing children? the wait for answers may well be maddening. mexico has a stunning backlog, an estimated 26,000 unidentified

bodies. and yet, when we visit the national forensics facility, they tell us they have only 25 technicians working on identifying remains. although the man in charge insists they do care deeply about their work. so when you're doing your work you're thinking of these families? >> always, always. they see the pain in the family, pause they are the same persons to collect samples from the families. they know their faces, because we go to the sites and take samples. we feel this, we know his pain. >> reporter: of course there is another way to find the disappeared. solve the crime and bring the perpetrators to justice. >> it's always hard, never gets easier. >> reporter: but, as lucy diaz knows, that is a struggle. we follow lucy on her monthly trip around mexico city to visit federal law enforcement

authorities. >> i do get fed up for a minute. i say oh, my god, i get all this disappointment and i feel down, depressed. you have to keep going. you can't stop. >> reporter: today, she's headed to various vetitiinvestigative agencies to see if there are any updates on her son luis, now missing for six years. she leaves empty handed. >> happens all the time. >> reporter: is it disappointing? >> i try not to think about it anymore, because that's exactly what they want. i get fed up. i get tired many of t. i get frustrated and then just don't come back again. >> reporter: so we decide to take lucy's case directly to the

president of mexico, lopez obrador, also known as amlo. he frequently campaigned with the family the of ties of promising to help. every day he holds a press conference. we've been following the case closely of lucy diaz, one of the most prominent mothers in the country involved for the search for the disappeared. we take a look at her case. it's clear there are many outstanding leads, and her allegation is that the police are simply refusing to follow up on these leads. if somebody with her resources and education can't get justice in this country, can anybody? and two, would you commit here

and now using your power to take a look at her case to see if you can move it forward? thank you. he promises that one of his top officials will personally reach out to lucy. [ speaking in spanish ] >> reporter: lucy catches the exchange on television. >> i hope that this will lead to a little bit more investigation in my case. >> reporter: i would think on one level, if the president of the country says all right, i'm going to pay attention to this case, you would think, all right, done. >> yeah. >> reporter: but i know how many times you've been disappointed. how do you set your expectations from here? >> if he doesn't do anything i'll be just massively disappointed this time, you know? because i never set my hopes so high.

>> reporter: it has now been nine months since the president of mexico promised to intervene in lucy's case. as of tonight, lucy says she has not received so much as a phone call. ted someone super quiet. yeah, and he wanted someone to help out with chores. so, we got jean-pierre. but one thing we could both agree on was getting geico to help with renters insurance. ♪ yeah, geico did make it easy to switch and save. ♪ oh no. there's a wall there now. that's too bad. visit geico.com and see how easy saving on renters insurance can be. a lot of folks ask me why their dishwasher doesn't get everything clean. i tell them, it may be your detergent... that's why more dishwasher brands recommend cascade platinum... ...with the soaking, scrubbing and rinsing built right in. for sparkling-clean dishes, the first time. cascade platinum. the ones that make a truebeen difference in people's lives.

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