A Reuters reporter saw Yusuf at a military barracks in the northern city of Maiduguri after his capture. Yusuf had no visible injuries and was standing up. He was later transferred to the city's police headquarters where he died.source -- Reuters AlertNet
"He has been killed. You can come and see his body at the state police command headquarters," Isa Azare, spokesman for the police command in Maiduguri, said.
Note that there is no explanation, nor regret, cited in the report.