AN AIR of mystery has long surrounded Abubakar Shekau, the head of Boko Haram, a guerrilla group whose campaign for an Islamist state in northern Nigeria has led to the deaths of about 3,000 people in the past four years. Most of what is known about him is gleaned from sermons he has posted on the internet. He has been the voice of Boko Haram’s most violent faction since its first attack on a prison, in the north-eastern state of Bauchi, in 2010. Clad in camouflage and body armour, flanked by Kalashnikovs and pointing aggressively into the camera, he calls for the application of sharia law across Nigeria.

On August 19th Nigeria’s security forces declared that Mr Shekau, who has led Boko Haram for the past three years, may be dead. They say he was shot in a gun battle on June 30th in the north-east, and may have died between July 25th and August 3rd, after fleeing east to Cameroon.

Yet in a video aired on August 13th, a man resembling the burly, thickly bearded Mr Shekau claimed responsibility for the most recent attacks. The army says the man in the video, which has not been independently verified, is an impostor. But this is the fifth time the rebel leader has been pronounced wounded or dead.

Mr Shekau had been second-in-command to Muhammad Yusuf, Boko Haram’s founder, who was killed in police custody in 2009. Since then he has radicalised the movement and overseen more deadly and co-ordinated attacks. The United States has offered $7m for information leading to his arrest. Some say he is 35 or 36, others that he may be 44; such uncertainty adds to his mystique. He lacks his predecessor’s charisma yet plainly wields power over an inner circle whose members pass his orders to the foot soldiers.

If he is truly dead, his passing would mark the end of an era for Boko Haram. Over time, it has splintered into factions, and it is unclear how much Mr Shekau co-ordinates them. If his death is confirmed, offshoots of the group may perhaps be willing to engage the government in talks and even to declare a ceasefire.

Yet since his alleged demise, at least 70 people have been killed in bombings and shootings in Borno state. Co-ordinated lethal attacks are still taking place, contradicting repeated military claims that the insurgents are being snuffed out. If Mr Shekau is still alive and reasserts his leadership, his allure will be greater still.