MAIDUGURI, Nigeria - Five days of fighting between government forces and a radical Islamist sect left dirt roads soaked with blood, buildings scorched and dozens dead, including the group's leader, but revenge attacks were feared even as the national police claimed victory.

Mohammed Yusuf, head of the Boko Haram sect, was killed on Thursday after he was found hiding in a goat pen at the home of his in-laws, but the circumstances grew murkier on Friday.

Police said Yusuf was killed in a gunfight but a Nigerian army officer disputed that.

"He was arrested alive," Army Col. Ben Ahonatu told The Associated Press on Friday. "There was no shootout."

Police, who invited local journalists to view Yusuf's battered corpse Thursday evening, insisted he was fatally wounded in combat.

"Mohammed Yusuf ... died in a gunbattle between armed sect members and a joint military-police force," said Christopher Dega, police commissioner of Borno state, of which Maiduguri is the capital.

A video obtained by AP Television News from police shows what authorities say is Yusuf's body. The corpse is in the middle of a street and the victim's hands are cuffed. The injuries were severe, with gaping wounds to sections of his arms and abdomen.

Bursts of gunfire can be heard in the background.

Human Rights Watch and Amnesty International called for investigations into Yusuf's death and other killings during the upheaval in predominantly Muslim northern Nigeria.

Emmanuel Ojukwu, spokesman of the national police, said Yusuf's death spelled the end of his group which espouses anti-Western views and had been gathering disciples for years.

"This group operates under a charismatic leader. They will no more have any inspiration," Ojukwu told AP. "The leader who they thought was invincible and immortal has now been proved otherwise."

But Charles Dokubo, analyst with the Nigerian Institute of International Affairs, said he expects more trouble.

"The rebellion is more than an individual," Dokubo said. "In as much as he was the leader, it does not mean this is over."

The 39-year-old Yusuf had managed to escape death on Wednesday along with some 300 followers as troops shelled his compound in the city of Maiduguri, killing about 100 people, including Yusuf's deputy.

Yusuf's death could provoke more violence, though the Boko Haram sect, sometimes called the Nigerian Taliban, is now likely in disarray.

Security forces thought they had already written the epitaph for the sect, back in December 2007 when Nigeria's military apparently crushed the group after it attacked police outposts in two northern states.

Jennifer Cooke, director of the Africa program at the Washington-based Center for Strategic and International Studies, said "poverty, unemployment and a state authority ... from which people feel alienated" have given rise to radical groups in Nigeria, a major oil producer and Africa's most populous nation.

"These new religious groups are fed up with a corrupt government, so people are turning to religion and extremism as an alternative to a failed state," Cooke said. "You could see a resurgence of this or another similar group."

Most Boko Haram members are young, poor and unemployed, although a few came from highly educated and elite families. They share anger that the introduction of moderate Shariah law in 12 northern states 10 years ago has not stemmed corruption that keeps most Nigerians impoverished while only a few prosper from the country's oil wealth.

Yusuf, a Western-educated member of the country's elite, encouraged his followers to rid themselves of all material wealth, but was chauffeured in a Mercedes all-terrain vehicle and amassed dozens of vehicles at his compound. A university graduate, he discounted Darwin's theory of evolution, claimed the world cannot be round because the Qur'an does not say that and credited Allah with creating rain.

In a wave of violence that began Sunday in Borno and quickly spread to three other northern states, Boko Haram -- which means "Western education is sacrilege" -- attacked police stations, churches and government buildings. The group is seeking the imposition of strict Islamic Shariah law in Nigeria, a multi-religious country.

On Wednesday, troops retaliated, killing about 100 people, half of them inside the sect's mosque. The bodies of barefoot young men littered the streets of Maiduguri on Thursday morning as security forces hunted militants.

Ibrahim Zakzaky, the head of Nigeria's Islamic Movement, said hard questions should be asked about the operation.

"The majority of those killed were innocent civilians," he maintained. "We believe the police just indiscriminately opened fire."

Amnesty International said Friday it had spoken to many family members of people detained by the Nigerian police and whose whereabouts are unknown.

"The organization fears that the missing individuals have been executed," the group said.