Official government account suggests Nkurunziza suffered a cardiac arrest while watching a game of volleyball in his home town and was taken to hospital where he died three days later.
Other narratives claim he may have been the victim of coronavirus which his wife contracted and was airlifted to Kenya.
The man who dominated Burundian politics for 15 years was to relinquish power in August after presiding over presidential elections in May.
He was poised to retire with a hefty $540,000 retirement package, a posh villa and the plump title of Supreme Guide to boot.
Toward the end of his second term as president Nkurunziza became a divisive figure in Burundian politics, causing public indignation when he ran and eventually won a controversial third shot at the presidency in 2015.
There were violent scenes in Burundi throughout that year when the country’s constitution was amended to allow him to prolong his stint as president.
He survived an abortive coup and was blamed for the purge that followed, forcing thousands to flee the country.
Burundians have been questioning the government’s explanation about the cause of his death from a supposed heart attack.
Nkurunziza shot to prominence in 2005 when he was elected by the country’s parliament to become president.
Hundreds of thousands of people had died during the country's civil strife between 1995 and 2005.
The former leader of the rebel Forces for the Defence of Democracy (FDD) had served in the cabinet as Interior minister
Although many Burundians will accuse his government of gross human right violations in 2015, Nkurunziza will be credited for being instrumental in restoring normalcy to Burundi.
A graduate in Sports Education, he was an ardent lover of football and gospel music.
Even as president he owned Halleluja FC and coached the main team originating from the Burundian military.
There are footage of him playing football. a game which continued to be organised across Burundi despite the outbreak of the deadly coronavirus and calls elsewhere in the world to encourage physical distancing.