started from sunya in china. at this time, the team from china has a small lead of two nautical miles. the teams are expected to reach auckland on saturday.

>> on the night of september 26th, 2014 students from a small school in the mexican state of guerrero were driving through the city of iguala...when they were stopped by police...and then fired upon 43 of them were never seen again

>> since the students were taken mexico has been consumed by protests. but the story goes deeper than the 43. tens of thousands of people have gone missing in mexico...as the government struggles to battle cartels. fault lines came here - before and after september's attack on the students - to try to find out why so many people are disappearing in mexico.

>> the school the missing students attended is here, the raul isidro burgos rural college of ayotzinapa - where they were training to become teachers. t's part of a network of schools known as the normales - or normalistas... ...founded in the aftermath of mexico's revolution to provide teachers for the country's poorest communities.

many of the students who were taken in september had just begun their first year at ayotzinapa. the classrooms they should be in...now serve as both a memorial and a base for the parents as they continue to search for their sons. mario, who lives nearly 10 hours away by bus came here the day after the attack when he found out his son cesar manuel was among the missing students.

the last time mario spoke to his son was the day of the attack.

students told us that they were preparing to travel to mexico city that day 3...to commemorate the killings of students by the army and police in 1968, something done annually. david said he was among the students headed to iguala that night, where they hoped to find more buses to get to mexico city.

in this video from that night, filmed by a student on his cell phone, the students are surrounded on either side, unable to escape. an ambulance arrives at one point - but is not allowed in.

omar says he and other students then drove to iguala to find out what happened and help their friends.

by the time they arrived the police had left - and the attack seemed to be over.

by the time the shooting was over six civilians were dead including three students - and 43 others were missing. >> with the exception of one student - alexander mora - neither the students nor their remains have been found.

>> watch more "faultlines" on demand or visit aljazeera.com/faultlines. >> sunday, the parents of captured american reporter austin tice. >> austin went missing in syria. >> campaigning for his release and maintaining hope. >> austin tice is alive. >> find him and get him home. >> a special "talk to al jazeera". sunday, 5:30 eastern. only on al jazeera america.

>> at one time i felt that selling cocaine was my purpose. >> as the amount of drugs grew guns came in. >> murder rate was sky-high. >> this guy was the biggest in l.a. >> i was goin' through a million dollars worth of drugs every day. i liked it. it's hard to believe that a friend would set you up. people don't get federal life sentences and beat them. >> they had been trafficking on behalf of the united states government. >> the cia admitted it. >> "freeway - crack in the system". only on al jazeera america. in the months that followed the

students disappearance dozens were arrested including the mayor of iguala - jose luis abarca - and his wife - who officials say ordered the attack on the students... ...allegedly believing they were going to disrupt an event they were holding that night - an allegation the students deny. after taking the boys off the buses, investigators say police piled them into the backs of their trucks and handed them over to a local cartel that had close links to the mayor and his wife. the case of the students ...is not an isolated one in mexico according to the government's own reports over 22,000 people have gone missing in mexico since 2006,

though human rights groups believe that number to be far higher. it's been three and half years since juana last heard from her daughter, brenda damaris - here it says i'm still alive.... find me it was late on a summer night when she called to say she'd been in a car accident just outside the city of monterrey. the family told us that as they were talking to her they heard a local policeman tell her to turn off her cell phone.

since damaris went missing no one has been prosecuted for her disappearance, leaving juana and the family to continue searching by themselves.

this is the case across mexico families left waiting...not

knowing if their loved ones are alive...or if they're dead. kidnappings are a source of income for cartels it's a way for them to extort civilians - but also to force people to work for them. with little help from officials, families of the disappeared across mexico have organized networks to support each other and try and help advance each other's cases.

with so few meaningful investigations one of the most important questions - why was this person taken - is rarely, if ever, answered.

federico mastrogiovanni is a journalist who's been researching the issue of disappearances over the past few years. >> why do you think there are so few investigations around disappearances here in mexico? >> watch more "faultlines" on demand or visit

aljazeera.com/faultlines. >> next monday a climate emergency. >> so a species could not be here in ten years. >> nasa steps in to help protect the future of the planet. >> the tropics regulate our climate. >> "techknow" heads to costa rica to see how one rainforest is fighting back. >> wow! some of these are amazing. >> "techknow's" team of experts show you how the miracles of science... >> this is my selfie, what can you tell me about my future? >> can affect and surprise us. >> don't try this at home. >> "techknow" where technology meets humanity. next monday, 5:30 eastern. only on al jazeera america.

>> in november, about a month after the 43 students disappeared mexico's attorney general said he believed they had been killed by cartel members... the bodies had been burnt, he said, and what was left had been put into plastic bags and tossed into a river just outside of iguala and it would be hard to identify or match the charred remains through dna. with so many disappearances in this region and potential dumping and burning sites, it may be impossible to ever get a full picture of what happened.

in the search for the students - carried out by officials as well as people from the community - one mass grave after another was discovered scattered through the hills. miguel angel is part of one of guerrero's community police forces formed in response to rising violence and local corruption - and the government's inability to curb it. they want to know if the remains they've found here could belong to the students...or to others that have gone missing in the area.

in the brush and trees there are chunks of tire rubber and empty bottles of gasoline miguel told us that when they find sites like this they notify the attorney general's office...but that it often takes as long as 2 days for government officials to come. it's not just miguel that

doubts the government's version though - independent forensic experts from argentina working on behalf of the parents say there are too many discrepancies...and not enough scientific evidence to prove the government's theory. the lack of trust in the ayotzinapa case isn't unusual. while there are some cases when remains in mass graves have been identified even when they have been it's often left families with more questions than answers.

a year after brenda damaris disappeared, local officials told juana that they had found her remains in a clandestine grave. >> all of these bodies were just piled together and thrown in a bag...you can see another skull, two skulls. but their belief that local police were involved in her disappearance - along with other discrepancies - made the family question if the remains they were given actually belonged to their daughter. her doubts led her here and to franco mora, a peruvian forensic doctor - he's going to exhume the remains the state gave the family. the remains lie in a grave marked by a cross with no name.

this is the first time an independent forensic test is being carried out to verify the states work in a disappearance in mexico juana told us she became suspicious after officials suggested that she cremate the bones immediately. the family placed the remains given to them by the state in a communal plot, not wanting to bury them in the family's section until they are certain it is her.

the team digs for nearly 2 and a half hours - until they reach the small gray box that holds the bones. the next step will be comparing the remains to dna from the family, though the results won't be known for months.