A new figure has emerged in the story of a Boston bomber's conversion to violent extremist Islam - a 23-year-old boxer from Canada who Tamerlan Tsarnaev met online and may have visited during his trip to Russia last year.
William Plotnikov, a Muslim convert from Toronto, could have spurred Tsarnaev to direct his against the United States, new reports reveal.
The Russian newspaper Novaya Gazeta reports that Tamerlan went to Dagestan - a Russia republic torn by jihadist terrorism - to join an Islamic militia and fight against Russian forces in July 2012.
One day after Plotnikov was killed by Russian security forces, Tamerlan fled to Moscow. The next day he was back to the United States.
Another contact Tamerlan had in Dagestan - Makhmud Mansur Nidal, 19 - was also killed by Russian forces during his six-month visit to to the war-torn region.
Tamerlan's family blames a red-haired Armenian convert known only as 'Misha' for turning the 26-year-old to extremist Islam.
However, Novaya Gazeta suggests Plotnikov may have turned Tamerlan against the United States.
'It seems that Tamerlan Tsarnaev came to Dagestan with the aim of joining the insurgents. It didn't work out..,' a security source told the newspaper.
Similarities: Plotnikov (left) and Tamerlan Tsarnaev (right) met online through a website associated with the World Assembly of Muslim Youth. Both suddenly adopted radical Islam in 2009, both were boxers and both were interested in fighting Russian forces in the Russian republic of Dagestan
'After Nidal and Plotnikov were destroyed and he lost his contacts, Tsarnaev got frightened and fled.'
Britain's Sunday Telegraph newspaper first reported Novaya Gazeta's claims.
Tamerlan and Dzhokhar Tsarnaev's parents moved them to the United States from the troubled Dagestan region years ago.
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The brothers are believed to be the lone perpetrators behind the April 15 attacks on the Boston Marathon that killed three people and wounded 270.
Tamerlan, the mastermind behind the attack, was killed April 19 after a shootout with police. Dzhokhar, 19, was captured by federal agents later that day in a boat in suburban Watertown, Massachusetts.
Dzhokhar told interviewers that Tamerlan planned the attacks to 'defend Islam' against the United States and was motivated by the wars in Iraq and Afghanistan.
Fighter: Tamerlan gave up boxing after he adopted radical Islam in 2009. Before that, he was a promising amateur fighter
The similarities between William Plotnikov - who was called 'The Canadian' by the other militiamen - and Tamerlan are uncanny.
Both men were competitive boxers as teenagers. Both seemed to have suddenly turned to radical Islam in 2009 and quickly became interested in violent jihad being waged in Dagestan - where Islamic militias are targeting the moderate Sufi Muslims and fighting Russian security forces who control the region.
Both were born in Russian republics and later moved to the West, where they struggled to fit in.
It is unknown whether Tamerlan and Plotnikov ever met in person. At one point, Tamerlan visited an aunt in Toronto - the same city where Plotnikov lived with his parents.
Leader: Tamerlan Tsarnaev, 26, (left) was the mastermind behind the April 15 Boston Marathon bomb attacks. Dzhokhar Tsarnaev, 19, (right) told police he was following his brother's orders
Plotnikov seized and interviewed by Russian authorities in 2010. At that time told them that Tamerlan was one of the people he communicated with online.
Novaya Gazeta reports that the two communicated via a site associated with the World Assembly of Muslim Youth, a non-governmental organization.
Plotnikov was then released by the Russians and went on to join an Islamic militia and take up arms against Russian security forces in Dagestan.
In February 2012, Tamerlan traveled to Dagestan. Novaya Gazeta reports that he was seen 'more than once' by Russian intelligence units with Makhmud Mansur Nidal, 19, a half-Palestinian Dagestani who is believed responsible for a twin bomb attack in the capital Makhachkala that killed 13 people.