There is no way of knowing exactly why there appears to be something of a breakthrough in the release of some of the 220-270 Chibok schoolgirls, most of them Christian, who were kidnapped by Boko Haram militants in April 2014.
One factor is surely the pressure being applied by the government and the new Nigerian president, Muhammadu Buhari, elected last year having promised to "crush" the terrorist organisation.
Another, however, is apparent divisions within Boko Haram itself.
In recent days, which have seen the release of 21 of the girls and speculation from government sources that a further 83 could be freed, there have been reports that a splinter group, allied to Islamic State, has said that the rest of the kidnapped Chibok girls were being held by the part of Boko Haram under the control of its figurehead Abubakar Shekau.
In other words, according to Reuters, Boko Haram has apparently split, with a large grouping departing from Shekau, over his failure to adhere to guidance from the Iraq and Syria-based Islamic State, which in August named Musab al-Barnawi as its new leader for West Africa.
Experts believe that the apparent breakthrough for at least some of the kidnapped girls – 40 of whom have reportedly been married and many forced to convert to Islam – has come about because of both national and international pressure.
Nationally, there are mixed reports of prisoner swaps. Military officers have said that the girls were exchanged for four detained Boko Haram commanders. But the statements were later denied by civilian officials. There are separate reports of a significant ransom being paid.
Internationally, there is a sustained outcry at the plight of the girls, of which Boko Haram leaders must be aware.
The deal which secured the release of 21 of the girls last Thursday was, after all, brokered by the Red Cross and the Swiss government.
The girls were brought from the north-eastern city of Maiduguri to the capital Abuja to meet state officials. And according to a spokesman for President Buhari, Garba Shehu, the 21 "are supposed to be tale bearers to tell the Nigerian government that this faction of Boko Haram has 83 more Chibok girls."
Shehu added: "The faction said it is ready to negotiate if the government is willing to sit down with them".
The state, it seems, is also willing to negotiate.
However, as hopes grow for a further tranche of released schoolgirls, there must also be fears for the fates of the girls who remain with the wing of Boko Haram led by Shekau.
The girls' capture was part of Boko Haram's seven-year-old insurgency to set up an Islamic state in the north of Nigeria, which has seen fighting that has killed some 15,000 people.
More than 910 schools have been targeted by the Islamist group, whose name means "Western [or non-Islamic] education is a sin". At least 611 teachers have been deliberately killed and another 19,000 forced to flee. At least 1,500 schools have closed.
In a video released in May 2014, then-Boko Haram leader, Abubakar Shekau, said women and girls would continue to be abducted to "turn them to the path of true Islam" and ensure they did not attend school.
The fighting has sparked a largely unreported refugee crisis with an estimated 2.2 million people, including 1.4 million children, displaced. Only around 10 per cent are in government-recognised refugee camps where there is some schooling. The other 90 per cent are living with friends and family members with little or no access to education.
The militants controlled a swathe of land around the size of Belgium at the start of 2015, but Nigeria's army has recaptured most of the territory. The group still stages suicide bombings in the north-east, as well as in neighbouring Niger and Cameroon.
