"The former detainees were in a classroom. They started screaming 'we are not Boko Haram. We are detainees!'" a witness told Amnesty at the time. "My neighbours and I saw the soldiers take the men to a place called 'no man’s land,' behind the University of Maiduguri. We watched as the soldiers opened fire killing all 56. They were killed in front of us. All of them." A New York Times report, which expressed skepticism that Boko Haram had attacked the facility at all, claimed that Nigerian warplanes and ground forces also indiscriminately opened fire as detainees and other civilians streamed out of the base. Based on witness testimony and other evidence, Amnesty estimated that Nigerian security forces had extrajudicially murdered more than 600 people, most of them unarmed, escaped detainees, around Maiduguri. Nigerian government accounts gave far lower death tolls.

The Maiduguri episode is just one example—albeit a particularly gruesome one—of alleged atrocities committed by Nigerian security forces, who have been fighting Boko Haram insurgents for five years now. The Islamist militants hold sway over vast swaths of northern Nigeria and have killed thousands in a campaign of bombings and attacks since 2009. "There's a lot of frustration, exhaustion, and fatigue among officers and [troops] based in the hotspots," a Nigerian security official told Amnesty this week. "Many soldiers are afraid to go to the battle fronts." As the conflict drags on, international observers like Amnesty, Human Rights Watch, and the U.S. State Department have increasingly condemned the indiscriminate arrests, torture, and extrajudicial killings of civilians and suspected militants by Nigerian security forces.

Nigeria's 130,000 active military personnel—in a country of 177 million people—bear most of the burden of fighting Boko Haram. But by many assessments, these soldiers are underequipped, undertrained, and underfunded. Rampant corruption hinders the army's morale and effectiveness, with reports of desertions and even infiltration by Boko Haram itself. During a March visit to Nigeria, UN High Commissioner for Human Rights Navi Pillay warned that human-rights violations by security forces "created fertile ground for Boko Haram to cultivate new recruits."

These issues complicate international efforts to help Nigeria find and rescue the 276 missing girls of Chibok, which have intensified ever since Boko Haram leader Abubakar Shekau released a video proclaiming that "God instructed me to sell them"—presumably into sexual slavery. Social media also helped spotlight the crisis after Nigerians created the Twitter hashtag #BringBackOurGirls; on Wednesday, it received the support of U.S. First Lady Michelle Obama. Even members of al-Qaeda, with whom Boko Haram is nominally aligned, have expressed disgust with the attack.