He was trying to help victims of the Nigerian jihad terrorist group Boko Haram (“Books Bad”).
He has been kidnapped. The culprits are rather painfully obvious. French-language article here (thanks to Bill).
Kidnapping infidels and releasing them for ransom or killing them, as well as enslaving them if that option is deemed most advantageous for the Muslims, is fully sanctioned in Islamic law: “As for the captives, the amir [ruler] has the choice of taking the most beneficial action of four possibilities: the first to put them to death by cutting their necks; the second, to enslave them and apply the laws of slavery regarding their sale and manumission; the third, to ransom them in exchange for goods or prisoners; and fourth, to show favor to them and pardon them. Allah, may he be exalted, says, ‘When you encounter those [infidels] who deny [the Truth=Islam] then strike [their] necks’ (Qur’an sura 47, verse 4)” “” Abu”l-Hasan al-Mawardi, al-Ahkam as-Sultaniyyah (The Laws of Islamic Governance), trans. by Dr. Asadullah Yate, (London), Ta-Ha Publishers Ltd., 1996, p. 192.