The BBC has obtained a photograph which shows that Mohammed Yusuf, the leader of the Boko Haram sect in Nigeria, was alive when captured by the army. They handed him over to the police. A few hours later, journalists were shown his bullet-ridden body. The police said he had been fatally wounded while trying to evade capture. Mr Yusuf's Islamic sect is blamed for days of violent clashes with security forces across northern Nigeria, which killed hundreds of people. Human Rights Watch in Nigeria have called for an immediate investigation into the killing of Mr Yusuf, 39, which they called "extrajudicial" and "illegal". On Friday, the army commander of the operation against the Boko Haram group, Col Ben Ahanoto, said he had personally captured Mr Yusuf and handed him over to the chief of police in Maiduguri, the capital of Borno state. He said Mr Yusuf had a wound in his arm - which is clearly shown in the photograph - which had already been treated. The police, however, insisted he had been fatally wounded in combat.