A YouTube account apparently belonging to Tamerlan Tsarnaev gives tantalising hints of his radicalisation before the Boston bombings, and includes a speech by a Russian militant cradling a gun, a bizarre attack on Harry Potter, and songs by a popular Russian rapper.

Tsarnaev created a YouTube channel in August 2012, shortly after returning to the US from Moscow. He spent six months in Russia last year between January and July, visiting his parents in Makhachkala, the capital of the Muslim republic of Dagestan. Tsarnaev also visited neighbouring Chechnya.

It is unclear if Tsarnaev met militant rebel groups during his trip. They have vehemently denied any link. His aunt said Tsarnaev's deepening interest in radical Islam pre-dated his Russia visit, with the FBI interviewing Tsarnaev inconclusively in 2011 after a tip-off from Russian authorities. By the time he arrived in Dagestan, he had grown a beard, prayed five times a day and had given up drinking, she said.

Whatever his links with Dagestani rebels, five months ago Tsarnaev posted two revealing videos. They feature a little-known jihadist leader, Abu Dujana, making a rambling speech to "Muslim youth". Abu Dujana wears military fatigues and holds a Kalashnikov. He speaks in Russian. Two other armed rebels – their faces hidden by scarves and balaclavas – sit next to him, against a black Islamist flag.

Abu Dujana appears to be from Imarat Kavkaz, a jihadist outfit allied to the main anti-Kremlin leader in the North Caucasus, Doku Umarov. His tiny group named itself after Rabini Kallikov, a local militant killed by Russian security forces in 2005 or 2006. In December, months before the Boston attacks, Russian police in turn killed Abu Dujana during a raid on his Makhachkala flat.

Cerwyn Moore, an expert on the insurgency in the North Caucasus at Birmingham University, said of Tsarnaev's video post: "He's obviously aware of some of the clandestine groups operating in Dagestan. This is a small sub-group. Abu Dujana is not a big player. Federal forces have been successful recently at killing all the top leaders." Chechen rebel groups pioneered the use of video messages from the late 1990s, well before al-Qaida, he added.

Tsarnaev listed the two videos under the category "terrorism". Later he – or someone else – deleted them. Other videos on his YouTube account star impressionable young men talking, in Russian, about their conversion to Islam: spiritual journeys of transformation that seem to echo Tsarnaev's own. One, Mikhail, is from Pyatigorsk, in the North Caucasus; another shares his experiences from a Yekaterinburg mosque.

There are also songs by Timur Mutsurayev, a religious Chechen singer whose ballads have been classified by Russian courts as "extremist". (One is titled: "Life is devoted to jihad.") Two videos feature Vasya Oblomov, a young rapper with a huge mainstream following. Oblomov sang in December at an anti-Putin rally in Moscow. His drole rhyming lyrics satirise the police, officials, and Russia's most ubiquitous problem: corruption. He condemned the Boston bombings after his videos surfaced as Tsarnaev favourites.

Andrei Soldatov, an expert on Russia's security services, said Tamerlan was already radicalised before his 2012 trip to Russia. "It looks like he was inspired via the internet and then maybe in Dagestan. So far there is no evidence he got in touch with anyone linked to terrorist activities in Dagestan. I'm in a mood to trust the militants' statements they [had] nothing to do with the attack: the insurgency in the North Caucasus has never attacked Americans. They are not legitimate targets."

The most curious video on Tsarnaev's playlist warns good Muslims not to allow their kids to watch Harry Potter. In what at first appears to be a Borat-like spoof, Sheikh Feiz Muhammad – a radical, bearded cleric based in Australia – denounces JK Rowling works. He declares: "This film glorifies paganism and evil ... It teaches your children the drinking of unicorn blood and magic."

Tsarnaev posted his last video two months ago. He subscribed to a UK-based channel called Allah is the One. Britain has also experience of Muslims being radicalised via the internet. The first case to come to light was Roshonara Choudhry, a gifted student, who dropped out from university after watching material from an extremist preacher on YouTube.

Choudhry went on to try and assassinate a British MP, Steven Timms, as punishment for supporting the Iraq war.

It emerged at her trial that Choudhry was radicalised after watching internet sermons given by Anwar al-Awlaki , the Islamist cleric who was based in Yemen, and whom the US eventually killed.

Material from al-Awlaki remains on YouTube. His extremist message continues to be spread from beyond the grave through the English-language terror manual he created, Inspire magazine, which is still disseminated via internet forums. The material was linked to three would-be suicide bombers convicted in February of plotting to carry out attacks in the UK which would have been more deadly than the 7/7 bombings in 2005. Police now monitor anyone trying to access Inspire on the internet.

What remains unanswered is why Tsarnaev's 2012 YouTube playlist did not ring alarm bells for the FBI. One clip shows young Muslim warriors parading with Kalashnikovs held about their heads, to booming martial music. The clues were all there.

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