Now Rahmatullah Azizi stands as a central piece of a puzzle rocking Washington, named in American intelligence reports and confirmed by Afghan officials as a key middleman who for years handed out money from a Russian military intelligence unit to reward Taliban-linked fighters for targeting American troops in Afghanistan, according to American and Afghan officials.

As security agencies connected the dots of the bounty scheme and narrowed in on him, they carried out sweeping raids to arrest dozens of his relatives and associates about six months ago, but discovered that Mr. Azizi had sneaked out of Afghanistan and was likely back in Russia. What they did find in one of his homes, in Kabul, was about half a million dollars in cash.

American and Afghan officials for years have maintained that Russia was running clandestine operations to undermine the U.S. mission in Afghanistan and aid the Taliban.

But they only recently concluded a Russian spy agency was paying bounties for killing coalition troops, including Americans, which the Kremlin and the Taliban have denied.