Some girls managed to escape shortly after the fighters stormed their school and hauled their classmates away. But Ms. Ali is the first girl to be found since the early days of the episode.
More than 200 girls who were taken from the school on April 14, 2014, are still missing. The mass abduction was one of the most notorious acts by a group that has rampaged through the north of Nigeria, burning entire villages and carrying out rapes, beheadings, lootings and other acts of violence.
A military spokesman on Wednesday said that one of the Chibok girls was among a group of people rescued by troops, claiming credit for the recovery.
According to the vigilante commander, Ms. Ali was with a baby and a man described as her husband. The commander said that the husband had been captured by militants as well, and that the two married while being held by Boko Haram. The couple apparently escaped the militants’ camp.
But in a news release late in the day on Wednesday, the military said the man was in fact a suspected Boko Haram terrorist who claimed to be the girl’s husband. The release described Ms. Ali as a nursing mother with a 4-month-old baby, a girl named Safiya.
Members of the vigilante group took Ms. Ali to Chibok, where her mother saw her and confirmed her identity, Mr. Aboku said. Other members of the community of Chibok also confirmed that Ms. Ali had been found. She told her family that the other girls from Chibok were still in the forest but that six of them had died.
Ms. Ali was in the custody of the Nigerian military in the town of Damboa, according to Mr. Aboku.
Hassan Usman, a Chibok resident whose niece is among the abducted schoolgirls, said he had seen the rescued girl arrive in Chibok in a car driven by local vigilante members from the neighboring town of Mbalala, where her family lives. The vigilantes took Ms. Ali to the marketplace in the town’s center, the same place a suicide bombing took place earlier this year.
“She was so happy to see her people,” Mr. Usman said. “People were so happy, so happy that, yes, there is hope these girls are alive. And once the government puts more effort, we will see some of them.”
Some local residents who saw her started crying.
Holding her baby, Ms. Ali talked with residents for about a half-hour, telling them she had been held in a village in the Sambisa Forest along with about 60 other female captives. Some of them were her classmates from Chibok; others were from other communities.
American officials have said that clusters of the schoolgirls have been located at times using a combination of local intelligence gathering, intercepted communications and drone footage.
But rescue operations have not been carried out, the officials said, because of fears that any ensuing battle with Boko Haram fighters would put the captives at risk, or incite retaliation against hostages still being held in other areas.
Mr. Usman said the rescued girl had described how Boko Haram tried to shield the hostages from aerial surveillance. “Anytime they sighted a fighter jet or any helicopter or military aircraft, they hide them under the ground so that it will prevent the military from seeing,” she told villagers, Mr. Usman said.
Ms. Ali was able to escape because the military began bombing the forest and the militants scattered, leaving her unguarded. Nigeria’s military this month launched a push into Sambisa called “Operation Sambisa Crackdown.”
Ms. Ali was in the custody of the Nigerian military and being taken to Maiduguri for questioning, according to the military.
The kidnapping of the schoolgirls captured the world’s attention. An international campaign with the hashtag #BringBackOurGirls drew in Michelle Obama and Malala Yousafzai, the Pakistani student who survived being shot in the head by the Taliban.
Genocide Watch is the Coordinator of Alliance Against Genocide. Founded in 1999, the Alliance is made up of over 50 organizations from around the world and was the first coalition of organizations focused completely on preventing genocide.