The parents of 43 students missing in Mexico are leading a march of thousands of people in the capital to mark one year since their disappearance.Many are carrying photos of their loved ones in Mexico City, demanding justice.
The parents want the government to hand over the investigation to a special unit under international supervision.
They dispute the government's account that the students were handed over by police in the city of Iguala to a criminal gang, which killed them.
A group of independent experts has suggested the students were killed because they unknowingly took control of a bus carrying illegal drugs, and the government did nothing to protect them.
Meanwhile, President Enrique Pena Nieto has announced the creation of a special team to look into the case.
'No impunity'The marchers are moving along Mexico City's Paseo de la Reforma towards the city's historic Zocalo Square.
"We came with a thirst for justice," student Sofia Rojas told the AFP news agency.
"There can be no impunity. Behind the 43 are thousands of disappeared."
At the scene: BBC's Katy Watson, Mexico CityThe protestors on the streets in Mexico City called the march "a day of indignation" - it allowed people to show their anger towards the government over the handling of the students disappearance.
Lots of people were carrying posters, saying "Out with Pena Nieto" and "No more disappearances and no more deaths".
There is a lot of anger and blame placed on the state for the student's abduction.
Earlier this week though, the president met the families and said he was on their side, that he too wanted to get to the bottom of what happened.
But speaking to the relatives of the missing ahead of the march, it is clear that there is a great deal of distrust and they do not think the government is supporting them.
The families are also demanding that the government look into the possible role of the army in the disappearance of the students.
The students disappeared on 26 September 2014, in Iguala in the southern Guerrero state.
They had gone there to gather for a commemoration in Mexico City.
The federal government has said local police from Iguala and the nearby town of Cocula had detained the students and turned them over to the local drug gang, which then allegedly killed them and burnt the remains.
But a team of international experts sent by the Inter-American Commission on Human Rights spent six months reviewing the government's investigation and found a number of flaws.
It concluded the bodies of 43 students could not have been burned at the rubbish dump in Cocula as the government maintained.
The government says forensic experts have identified two of the students from the burnt remains recovered from the rubbish dump.