One of the brothers suspected of the Boston Marathon bombings had direct contact with Chechen terrorists – and was ‘monitored’ by investigators for five years. The Mail on Sunday has learned that the FBI put Tamerlan Tsarnaev, 26, under surveillance after receiving an explicit warning from the Russian intelligence services.

But despite apparently telling his mother that Tamerlan was an ‘extremist’ leader, the FBI eventually discounted the possibility that he was a threat....

US congressmen have expressed concern that the tip-off about Tamerlan to the FBI from Moscow may not have been properly followed through.

Yesterday the brothers’ mother, Zubeidat, said the FBI once told her that Tamerlan was ‘really an extremist leader and that they were afraid of him’. She added: ‘He was controlled by the FBI for five years. They knew what my son was doing. They were following every step of his.’ And his father, Anzor Tsarnaev, said investigators warned his son: ‘We know what sites you are on, we know where you are calling, we know everything about you. Everything. We are checking and watching.’

Despite all this, the FBI found no substantive evidence that he was engaged in terror-related activities though they continued to ‘monitor his internet use and contacts’.

According to an intelligence source, Russia remained convinced that Tamerlan, an ethnic Chechen, was in ‘direct contact’ with Islamist militants, most likely based in the strife-torn southern Russian region of Dagestan, where he lived for two years with his family prior to moving to the US.

During a six-month visit to Russia last year – a trip US investigators are investigating – it is understood Tamerlan visited Dagestan, which is now regarded as more unstable than Chechnya.

One theory is that Tamerlan and Dzhokhar, who was in thrall to his older brother, may have been ‘inspired’ by a rebel leader known as Russia’s Bin Laden.

Doku Umarov, like the Tsarnaev brothers, is an ethnic Chechen from the war-torn Caucasus region that lies between Europe and Central Asia. He has been accused of masterminding some of the worst terrorist atrocities in Russia, including suicide bombings carried out by two women on Moscow’s Metro system in 2010 which killed at least 40.

Significantly, while Umarov was originally fighting only for Chechen independence he has more recently embraced a wider jihadist agenda.

Chechen expert Dr Carlo Gallo, the founder of London-based political risk firm Enquirisk, explained: ‘Umarov has made statements in which he has said that the enemy of Islam is not just Russia but America, though the insurgents have never conducted significant operations outside Russia.’

It raises the terrifying prospect of further atrocities being carried out across the globe by disaffected individuals inspired by the jihadist rhetoric of the former Chechen leaders.

Last night as calls were made for Dzhokhar to be classified as an ‘enemy combatant’, the brothers’ uncle, Ruslan Tsarni, said Dzhokhar had been ‘used’ by his older brother who had fallen under the influence of a US-based radical of Armenian descent who ‘brainwashed’ him.

Mr Tsarni said that when he met his nephew in 2009 he was troubled by his transformation.

‘I was shocked when I heard his words, his phrases. He claimed he would just put everything in the will of God. It wasn’t devotion, it was, as it’s called, being radicalised.’

For many years, though, Tamerlan and his younger brother had seemed settled in the United States. They were popular at school and excelled at sport.

But it became clear yesterday that it was a series of setbacks in Tamerlan’s personal life that rendered him increasingly bitter. Individually, none seems particularly significant, but cumulatively they were devastating and caused him to turn against his adopted homeland.

Tamerlan was a promising boxer, possibly destined for the US Olympic team, but his dream was shattered by a back injury. At the same time he could only manage to secure menial work, though he was considered bright at school.

He was devastated when his best friend was killed in 2011 in an unsolved murder and then came an incident which investigators believe is particularly significant.

He was arrested for assaulting his girlfriend in 2009 – which scuppered his chance of obtaining American citizenship....

Last night the brothers’ parents defended them, as one lay dead and the other critically ill but stable in hospital. Mr Tsarnaev said there was nothing suspicious about his son’s 2012 visit to Dagestan.‘He wasn’t occupied with anything. He was just visiting relatives,’ he said. ‘I knew what he was doing, where he was going.

‘I raised my children right,’ he added. ‘This is all lies. These are my children. I know my children.’

Tamerlan is thought to have grown a long beard after returning to Boston from his trip to Russia.

Police believe he shaved it off some weeks ago because he wished to remain inconspicuous as he planned the bombing. While denying involvement in any militant form of Islam, Mr Tsarnaev confirmed that the family was religious. ‘What kind of Islam? In Islam we have purity,’ he said.

‘We do what we’re supposed to. We pray five times a day. That’s it.’

And denying that her sons would have hidden any secret extremist leanings from her, his wife said: ‘That’s impossible. My sons would never keep a secret. Never ever is this true, my sons are innocent!’

Mr Tsarnaev added that he had spoken to Tamerlan after the marathon outrage, telling him: ‘Thanks to Allah you were not close to there and did not suffer.’...

... We pray five times a day. That’s it.’

"But that a camel-merchant should stir up insurrection in his village;
that in league with some miserable followers he persuades them that he talks with the angel Gabriel;
that he boasts of having been carried to heaven,
where he received in part this unintelligible book,
each page of which makes common sense shudder;
that, to pay homage to this book, he delivers his country to iron and flame;
that he cuts the throats of fathers and kidnaps daughters;
that he gives to the defeated the choice of his religion or death:
this is assuredly nothing any man can excuse,
at least if he was not born a Turk,
or if superstition has not extinguished all natural light in him."