Amnesty International added a troubling twist to the saga of the kidnapping of over 240 Nigerian school girls on Friday. According to the organization's sources, Nigerian security forces had advance warning that Boko Haram was launching an attack on the Chibok school more than four hours before it happened, but they failed to do mobilize to stop it. If the reports are correct, it should only spark more outrage against the Nigerian government's inability to rescue the girls and put down the threat from Boko Haram.

Amnesty's timeline, based on interviews with multiple unnamed sources, has the Nigerian military headquarters in Maiduguri learning about the impending attack at 7 a.m. on April 14. Four hours later, Boko Haram militants began an assault on a state-run boarding school in Chibok, kidnapping hundreds of girls between the ages of 16 and 18. 

The military did not send reinforcements to Chibok despite knowing about the attacks, in part because of a " fear of engaging with the often better-equipped armed groups," Amnesty wrote. Nigerian authorities haven't yet commented on Amnesty's report, the BBC notes

U.S. military officials arrive in Nigeria on Friday to assist the country in its so-far unsuccessful search for the girls, as Nigerian President Goodluck Jonathan faces mounting criticism for his government's response to the kidnappings. 

Update: ABC is reporting that Nigeria has denied Amnesty's report