Two years ago 276 girls were abducted by the deadly Boko Haram sect from their dorms in a secondary school in north-eastern town Chibok of Borno state.
Their abduction sparked one of the biggest global social media campaigns, with tweeters using the hashtag #BringBackOurGirls.
But most of the girls are still missing.
NAIJ.com looks at what we know:
How it happened
The Boko Haram insurgents attacked a school in the late hours of April 14, 2014, where girls from surrounding areas were preparing to take the exams.
Many schools in the state were closed as the deadly sect was targeting them because of their opposition to Western education.
The terrorists arrived in the town late at night in a blaze of gunfire and headed for the school where they raided the dormitories and loaded 276 girls on to trucks.
Fifty-seven of the schoolgirls managed to escape within hours of their abduction, mostly by jumping off the trucks and running off into the bushes. 219 are still missing.
Why the Boko Haram abducted them?
Girls and women kidnapped by the Islamist group have defined life in captivity which includes forced marriage and labour, rape, torture, psychological abuse and religious conversion.
Since 2009 thousands of women and girls have been captured and held in militant camps. Many have been targeted because they are Christians or attending school.
One of the escapes also said that the Boko Haram forced the girls to go to school and to learn Quran
When the Chibok girls were last seen?
CNN has released the video on April 13, that show 15 of the abducted girls alive and looking well.
The girls in a black robes said they were being treated well but wanted to be with their families.
The video was reportedly recorded on the Christmas Day of the year 2015 as a part of the negotiations between the insurgents and the Nigerian government.
Shortly after the kidnap in May 2014 the Boko Haram unveiled the video of about 130 of them gathered together reciting the Quran.
What has been done for their release?
Five month after their abduction the government of Goodluck Jonathan announced that a ceasefire had been negotiated along with an agreement to release the girls.
However, later Boko Haram leader Abubakar Shekau mocked the claim, saying the girls had converted to Islam and been "married off".
Since President Muhammadu Buhari came to power the insurgents have been driven from towns and villages to their hideouts in the Sambisa forest - which cannot be accessed by road.
The Nigerian army has freed thousands of people from the captivity, yet there are still no information about whereabouts of any of the 219 girls.
Buhari has also ordered a new probe into the kidnapping.
Meanwhile, there are too many things that we don’t know.
We don’t know when the Chibok girls will return. The presidency stated the negotiations for their release are ongoing. However, while the incumbent government considers the return of Chibok schoolgirls a priority, it cannot be specific on when that will happen.
We don’t know the whereabouts of the missing girls. President Buhari during his first media chat state that there no reliable intelligence on the location of the Chibok girls, kidnapped by the Boko Haram in 2014.
We don’t know how many of them are still alive. One of the Boko Haram survivors has revealed that the Nigerian army accidentally killed five of the Chibok girls during the clearance operation of Boko Haram camp. At the same time, Ahmad Salkida, the journalists with access to the group’s commander, has said that investigation shows that only half of the girls are alive.
According to the latest report of the United Nations Children’s Fund the use of the child bombers by the deadly Boko Haram sect is on the rise. But we don’t know, if these girls are from the Chibok school.