WASHINGTON — In the winter of 2014, an Afghan with links to top Taliban leaders approached Afghanistan’s intelligence service with a startling tip: Mullah Muhammad Omar, the secretive leader of the Taliban, had died in a hospital in Karachi, Pakistan.

The tip left the intelligence service, the National Directorate of Security, with a mystery that would take 18 months to begin unraveling. But even with the Taliban confirming on Thursday that the man they called Emir al-Momineen, or Commander of the Faithful, was dead, American and Afghan officials said they were just starting to piece together the story of Mullah Omar’s final years and of his demise.

In interviews, Afghan, American and European officials offered insight into why it took so long to determine that Mullah Omar was dead: He may have been one of the world’s most wanted men — he carried a $10 million American bounty on his head — but by 2014 few people outside Afghanistan seemed to want him enough to put much effort into finding out whether he was dead or alive.

American officials said they had long ago come to believe that Mullah Omar’s role in the insurgency was primarily spiritual, and that he had little to no operational control over the Taliban. In an interview last year, a former American military commander went so far as to compare Mullah Omar to the medieval Spanish commander El Cid, whose corpse, according to legend, was suited with armor and propped up on a horse to bolster Spanish troops fighting the Moors.