Nigeria, March 14 -- Salamatu Salihu holds her face in her palms, weeping. Her next words were a quiet and desperate plea for forgiveness.

"I want everyone to forgive him," said the 70-year-old mother whose son, Idris, had been unmasked as a terrorist collaborator. The last time Mrs Salamatu saw him was early last year, when soldiers stormed their Kemanji village and arrested civilians alleged to have collaborated with Ansaru terrorists, locally known as the Mamuda group.

Since that incident, Mrs Salihu, a widow, has lived under a cloud of suspicion. Villagers were reluctant to lead this reporter to her home. The only person who agreed to help did so cautiously, offering only vague verbal directions, rather than personally guiding the w...