Parents raised and paid an undisclosed ransom to free the students, who were among more than 100 taken on July 5 from Bethel Baptist High School, officials say.
Ibrahim Zakzaky, founder of Islamic Movement in Nigeria, his wife Zeenah Ibrahim, acquitted of all eight criminal charges, says their lawyer.
Heavily-armed gangs in northwest and central Nigeria have stepped up attacks in recent years, kidnapping for ransom, raping and pillaging.
Nigerian army rescued 180 people in the early hours of Friday, but around 30 male and female students remain unaccounted for after gunmen attacked a forestry college in northwestern Kaduna state overnight.
Gunmen from gangs known for kidnapping and cattle rustling kill at least 19 people in Birnin Gwari and Kajuru villages in Kaduna state, officials say.
The attack took place in Kukum-Daji village in Nigeria's Kaura distric, targeting a wedding party at one of the community houses.
Around 100 armed assailants reportedly stormed into the villages of Kerawa, Zareyawa and Minda in Kaduna state at dawn on Sunday, gunning down residents, burning and looting homes.
Horror stories are emerging about life in a two-storey house in northern city of Kaduna as authorities try to find families of some 400 victims, men and boys, who often spent years at the site.
Nigeria's two main political parties condemn electoral commission decision to postpone presidential election until February 23 over "challenges." Meanwhile, authorities in Kaduna state report dozens of killings in a wave of violence.
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