Nigerian authorities promise an investigation and workers remain at the rubble and dust-filled scene of a school building collapse in Jos, in the central Plateau State, which left at least 21 dead and scores more injured. "Everybody must be responsible for human life, we cannot afford this kind of mishap again," says Caleb Mutfwang, Plateau State governor, during a visit to the site. “As a layman I know that there needs to be a proper mixture of sand and cement, what I can see here is, is pure sand.” IMAGES AND SOUNDBITES