Federal government says 82 Chibok schoolgirls are free more than three years after a mass abduction by Boko Haram extremists. It is the second group release; Nigeria announced in October that 21 girls had been freed after negotiations with the extremists. 

The kidnapping shocked the world and put tremendous pressure on Nigeria's government to counter Boko Haram and free thousands who have been taken captive over the years. Here are some of the key events surrounding the Chibok crisis:

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April 2014: Boko Haram extremists kidnap 276 schoolgirls from Chibok in northern Nigeria, the region where the insurgency emerged several years ago.

November 2014: Extremists seize Chibok, and Nigerian army takes back the town.

May 2015: New President Muhammadu Buhari is sworn in, pledging to tackle Boko Haram "head-on."

April 13, 2016: Boko Haram video appears to show some of the Chibok girls, and tearful mothers recognize their daughters.

May 18, 2016: Relative says one of the Chibok girls is found, pregnant, in a forest; pressure grows on Nigeria's government to rescue the others.

Aug. 14, 2016: Boko Haram video says some Chibok girls are killed in airstrikes and demands release of extremists in exchange for the other girls' freedom.

Oct. 13, 2016: Spokesman for Nigeria's president confirms 21 Chibok girls have been freed, a result of government negotiations with Boko Haram. Nigeria's government says another 83 girls would be released "very soon."

Nov. 5, 2016: Military announces the first army rescue of a Chibok girl, during a raid on a forest hideout.

Dec. 24, 2016: Nigeria's president declares that Boko Haram has been crushed, driven from its last forest hideout.

Jan. 5, 2017: Nigeria's army says soldiers find one of the schoolgirls wandering in the bush near the forest stronghold.

April 14, 2017: Nigerians mark three years since the mass abduction.

May 6, 2017: Nigeria's government says another 82 schoolgirls are released.

AP