The militants kidnapped 276 schoolgirls. Several dozen of them were able to escape. But two years later, even as the Nigerian, Cameroonian and Chadian militaries have pushed Boko Haram out of many of its former strongholds, 219 of the girls remain missing.
On Wednesday, CNN released an apparent proof of life video of fifteen of the girls, reportedly filmed last December. They wore flowing headscarves and stated their names. "We are all well," one of them said.
It was a rare window into their condition, but it raised as many questions it answered. The video alluded to a possible negotiation with the Nigerian government, but those details remain unclear. And many Nigerians wondered why it took so long for even the parents of the girls to see a video confirming they were still alive.
Where are they?
"I assure you that I go to bed and wake up every day with the Chibok girls on my mind," Nigeria's president, Muhammadu Buhari, said earlier this year.
But his efforts have not resulted in the return of any of the girls. Thousands of other Boko Haram victims have been released, recounting stories of forced marriage and sexual slavery. But not the Chibok girls. Most Nigerian and Western officials say the girls have been taken to a remote part of the Sambisa forest, a former game reserve in northeastern Nigeria, where they are being closely guarded by the militants.
Here's what we know about Boko Haram's reign that might help us understand what the missing girls have endured, and what would await them if they are rescued.
1. While militants have publicly accused Nigeria's secular government of being an affront to Islam, their victims say the group's members appeared much more interested in expanding their campaign of sexual violence than governing their self-proclaimed caliphate. Many of Boko Haram's victims became pregnant while in captivity. Most experts expect that the majority of the Chibok girls have already delivered the babies of their captors. And if they are released, like the other victims, they will likely be regarded with deep suspicion.
2. Boko Haram has leveled a number of the cities and villages that it once occupied, leaving more than 2 million people without homes. In Chibok, homes were burned to the ground. The secondary school was destroyed. The Nigerian government says it has begun rebuilding the part of the country ravaged by war: a multibillion-dollar project. But so far there is little evidence of progress.
3. Some girls abducted by Boko Haram have recently carried out suicide bombings. The number of children involved in such blasts grew tenfold, from four in 2014 to 44 in 2015, according to a report released by the U.N. children’s agency on Tuesday. Many Nigerians wonder: Were the Chibok girls brainwashed by their captors? Will they be forced into becoming attackers themselves?
4. The Nigerian military's campaign to dislodge Boko Haram might not be enough to locate the girls. The army has proven itself capable of conducting offensives in cities and towns, but the Sambisa forest is another tactical challenge entirely — dense, remote and vast. The leader of a different group, the Lord's Resistance Army, Joseph Kony, has been lurking for years near the borders of Sudan, South Sudan and the Central African Republic. The forces trying to find him include 100 U.S. troops. But the effort has yielded nothing. Some say that's a cautionary tale for the quest to find the Chibok girls and Boko Haram's top leadership. That top leadership, by the way, includes a number of teenage boys, according to the Nigerian military.