McClatchy has confirmed some of its contents but had been unable to locate anyone with the name "Seva Kapsovich" who matched Steele's description in the dossier. Then McClatchy noted inconsistencies in the spellings of various names in the dossier. That prompted a search for alternate spellings of "Kapsovich" in Cyrillic, the alphabet of the Russian and other Slavic languages. That turned up references to Kaptsugovich and Russian media accounts of his prior convictions, which matched the description laid out in the dossier.

A shadowy figure, first nabbed in 2001

Kaptsugovich was first arrested on pedophilia charges in Russia in March 2001 and was sentenced in January 2004 to 11 years in Solikamsk prison, known in Russia as a tough lockup. The arrest came about the same time the United States and Russia announced a successful joint effort called Project Blue Orchid that smashed an international pedophilia ring.

The joint law enforcement effort was shocking because it involved pedophiles from the United States and elsewhere traveling to Russia to have sex with young boys who had been plucked from poor rural homes on promises of a better life in the city. Instead, they were sexually abused and images of the horrific acts sold across the globe.

Sevastyan Kaptsugovich, believed now to be at least 45, was released before his full sentence was completed. He made headlines again when he was convicted a second time, on Feb. 14, 2013, for similar crimes and sentenced to more than 18 years in a penal colony. Sordid details of his trial in the city of Perm were published in the media outlet Komsomolskaya Pravda, where one of the few public photos of him appeared. His legal documents do not appear in RosPravosudie, a website and database that boasts information on more than 100 million Russian legal cases.

Local newspapers at the time said Kaptsugovich was a history teacher and the son of Igor Kaptsugovich, a noted academic and former rector of the Perm Pedagogical University in the Urals region, more than 700 miles east of Moscow. Attempts to reach the father through the university were unsuccessful.

Signs of being forced to cooperate

The 35-page dossier, which was published in full by BuzzFeed and contains a number of as-yet-unverified allegations, suggested that Kaptsugovich had been forced to cooperate with the FSB in hacking U.S. computer systems. It didn't reveal how he was involved, however.

But there are hints in the document, given his background in placing child pornography on the internet. The dossier said the hackers had used "botnets and porn traffic to transmit (computer) viruses, plant bugs, steal data and conduct 'altering operations' against the Democratic Party leadership." Botnets are electronic computer networks that can be programmed to carry out any number of functions, including sending massive amounts of data to overwhelm a website and effectively shut it down.

Suspect in prison when hacking took place

McClatchy has confirmed through a Russian human rights activist that Kaptsugovich is imprisoned in a facility known as IK-29 near the village of Sorda in the region of Kirov. That's about 500 miles northeast of Moscow.

"I did visit IK-29 on Feb. 17 of this year. During the visit I saw Sevastyan Kaptsugovich," Arthur Abashev wrote to McClatchy. "Indeed, he is an inmate there, and he works in the prison administration office. He does not have access to the internet, a computer or a mobile phone. He only has access to the landline phone."

Abashev is a member of the Public Monitoring Commission, a remnant from the Boris Yelstin era, soon after the collapse of the Soviet Union. It enjoys semi-official status as a rights group that monitors conditions in prison and labor camps and issues reports to the government.

Given that Kaptsugovich doesn't appear to have computer access, said Abashev, it is "unlikely that he would be involved in the hacking attacks."

'The truth is hidden in the shadows'

So why then would the dossier's author, a former MI6 agent in London and a well-regarded Russia specialist, mention Kaptsugovich? And how could a prisoner held in a remote penal colony have aided in a hack that hangs like a dark cloud over last year's U.S. presidential election?

"The truth is hidden in the shadows," mused Pavel Vrublevsky, a Russian internet pioneer who has run afoul of Russian intelligence and law enforcement agencies. Vrublevsky founded an online payment company, Chronopay, and recently served a jail term after being convicted of ordering a hacking attack on a competitor, a charge he insisted was drummed up.

Progammers arrested alongside pedophile

Like many references in the dossier, there's no obvious answer to why Kaptsugovich is named, and Steele hasn't broken his silence. The ex-spy faces a lawsuit in London from the other person named in the document as having been compromised into hacking, Aleksej Gubarev, a Cyprus-based Russian internet executive with operations in the United States.

There are, however, clues. Articles in Russian-language online publications said three other men charged in 2013 with Kaptsugovich were computer programmers. And police had said Kaptsugovich ran a network of pedophilia websites.

Russia's top cyberspy charged with treason

And there are events on the periphery. Was the recent arrest on treason charges of Col. Sergei Mikhailov, a top cyberspy for the FSB, the successor to the KGB, related to the dossier and its allegations about the hackers? Mikhailov and his underling, Maj. Dmitry Dokuchaev, were accused of collaborating with the CIA just weeks after the Obama administration publicized its conclusions that Russia had meddled in the U.S. presidential elections.

Russia media accounts said Mikhailov, who the accounts said was deputy director of the FSB's Information Security Center, was arrested and led out of his nine-story building with a bag over his head, a shaming tactic at the spy agency.

An international firestorm

U.S. law enforcement authorities have had the dossier since last July. It originally began as a compilation of political research and was paid for by Trump opponents in both major U.S. political parties. The dossier is part of a broader interagency investigation, first reported by McClatchy, into potential links between the Trump campaign and Russia, and subsequently leaks of classified information.

An ongoing investigation by McClatchy has shed light on some of the dossier's allegations, including the use of Russia's pension system to pay hackers and how a low-key diplomat in Russia's embassy in Washington has gotten caught up in the international firestorm.

Former KGB chief, named in dossier, found dead

Other seemingly unrelated events have involved the dossier. Mikhailov's unceremonial arrest in early December came just weeks before the death of another well-connected Russian who was a possible source of information in the dossier. Former KGB chief Oleg Erovinkin was found dead in his car in a Moscow alley on Dec. 26. He was chief of staff to Igor Sechin, the powerful head of Russia's state oil company Rosneft and a go-between for Sechin and Russian leader Vladimir Putin. Erovinkin matched the description in the dossier of a source close to Sechin, who the dossier says met with Trump campaign adviser Carter Page. Page denies the two ever met.

Spy agency known to work with criminals

That a Russian spy agency would work with a convict like Kaptsugovich to hack into computers in the United States is not farfetched, given the FSB's well-documented tolerance and even embrace of criminal organizations.

A recent study by New York University professor Mark Galeotti documented how Russia's state security apparatus works with criminal gangs at home and in Europe for intelligence-collection activities and to influence politics.