'Thisday' newspaper quoted a military source as voicing his reservations over the breach in communications and the hasty manner in which the military in Maiduguri, Borno State, broke the news without getting clearance from headquarters.
Moreover, observers noted that Shekau was first reported dead after the killing of the founder of the group in 2009 but later emerged to lead the group.
Shekau carries a reward of USD 7 million on his head.
But Shekau appeared on a video on August 12 accepting responsibility for several attacks occurred during last two month.
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Despite military's claim that the video was dramatised by an impostor, the fact that there was no evidence like a photo provided to prove his death made people to doubt army claim.
"I don't know why he (Lt-Col Sagir Musa) is in a hurry to announce this because Defence Headquarters have the same documents (about Shekau's death) here but they (DHQ) are still analysing it to ensure that the information is real," a source was quoted as saying.
More than 2,000 people have been killed since 2009 when Shekau inherited the leadership of the sect from its founder, Muhammed Yusuf who was killed in police custody.
In May, President Goodluck Jonathan declared a state of emergency in three out of the 36 states in a bid to stop the insurgency.
Boko Haram has vowed to introduced an Islamic system in most or if possible all parts of Nigeria by force.