Nigeria's declaration of victory over Taliban-style militants was overshadowed last night by demands for an inquiry into the "extrajudicial killing" of the sect's leader.
The bullet-riddled body of Mohammed Yusuf, head of the Islamist sect Boko Haram, was shown to journalists hours after police announced his capture at the end of a four-day manhunt.
Emmanuel Ojukwu, a national police spokesman, said: "This group operates under a charismatic leader. They will no more have any inspiration. The leader who they thought was invincible and immortal has now been proved otherwise."
But the triumphalism was punctured by conflicting accounts of how Yusuf died. Colonel Ben Ahanotu, commander of the military operation against Boko Haram, who claims he personally captured Yusuf, said that he had been unarmed and gave himself up willingly.
"All I know is that in the attack, I was able to pick him up from his hideout and hand him over to police," he told the BBC. "I asked him why he did what he has done and his response was that he would explain to me later. But he was OK. As I got him alive, I handed him over to the authorities."
The regional police assistant inspector-general, Moses Anegbode, had earlier told Nigerian television that Yusuf had been "killed by security forces in a shoot-out while trying to escape".
A policeman reportedly said that Yusuf "pleaded for mercy and forgiveness before he was shot".
Pressure groups demanded an investigation. Eric Guttschuss, of Human Rights Watch, said: "The extrajudicial killing of Mr Yusuf in police custody is a shocking example of the brazen contempt by the Nigerian police for the rule of law."
Another Human Rights Watch researcher, Corinne Dufka, added: "The Nigerian authorities must act immediately to investigate and hold to account all those responsible for this unlawful killing and any others associated with the recent violence in northern Nigeria."
Dora Akunyili, Nigeria's information minister, insisted that the government "does not condone extrajudicial killings" and steps would be taken to find out "exactly what happened".
Akunyili also described Yusuf's death as "positive" for Nigeria. She told the BBC: "What is important is that he [Yusuf] has been taken out of the way, to stop him using people to cause mayhem."
Analysts said it was not clear whether Yusuf's death would end the violence or inspire revenge attacks by the sect, which seeks the imposition of strict sharia law.
It is thought that more than 300 people have died in this week's violence. Some estimates put the figure at 600, although there has been no official confirmation. The Red Cross said about 3,500 people had fled the fighting and were being housed in its camp.