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…

U.S. intelligence reports named Mr. Azizi as a key middleman between the G.R.U. and militants linked to the Taliban who carried out the attacks. He was among those who collected the cash in Russia, which intelligence files described as multiple payments of “hundreds of thousands of dollars.” Those files were among the materials provided to Congress this week…

Afghan officials said prizes of as much as $100,000 per killed soldier were offered for American and coalition targets.