Tamerlan Tsarnaev, the eldest brother, subscribed to publications containing articles about government conspiracy theories and white supremacy. He also had reading material on mass killings.

Until now the Tsarnaev brothers were widely seen as straightforward radical jihadists.

Panorama has spent months speaking exclusively with friends of the bombers to try to understand the roots of their radicalisation.

The programme discovered that Tamerlan possessed articles which argued that both 9/11 and the 1995 Oklahoma City bombing were government conspiracies, and another article about "the rape of our gun rights".

Reading material he had about white supremacy commented that "Hitler had a point".

Literature Tamerlan had about mass killings, explored what motivated them and noted how spree killers murdered and maimed calmly.

He was also in possession of literature about US drones killing civilians, and about the plight of those still imprisoned in Guantanamo Bay.

Panorama: The Brothers who Bombed Boston will be shown tonight at 8.30pm on BBC One. The Tsarnaev brothers, ethnic Chechens, spent their early years moving around a troubled region of Russia torn by a violent Islamic insurgency.

But for the last decade they lived in Cambridge, near Boston.

The brothers’ friends told us Tamerlan turned against the country after becoming frustrated when his boxing career faltered because he did not have American citizenship.

Their friends wouldn’t all speak openly because they were afraid of being viewed as associated with terrorism.

‘Mike’ spent a lot of time in the brother’s flat.

“He (Tamerlan) just didn’t like America. He felt like America was just basically attacking all Middle Eastern countries… you know trying to take their oil.”

Dzhokhar Tsarnaev, Tamerlan's younger brother who has been charged with the bombings, scrawled a note shortly before his capture stating: "We Muslims are one body. You hurt one you hurt us all."

Friends say the younger brother smoked copious amounts of pot and rarely prayed.

‘Tito’ told us Dzhokhar’s older brother dominated him and didn’t approve of his ‘party lifestyle’.

“He (Dzhokhar) was intimidated that would probably be the best word. He took him very seriously. He was an authority.”

The FBI is still investigating the brothers, but the House Intelligence Committee in Washington is being briefed on Tamerlan’s connections.

The committee Chairman Congressman, Mike Rogers said he believes the brothers’ mother, Zubeidat Tsarnaev, was involved in his radicalisation.

He said: “I believe after looking at all that I have seen, that his mother was involved and probably was involved in bringing him along in radicalisation.”

“He had family members encouraging we know that for sure,” he said.

Zubeidat Tsarnaev denies the allegations.

Tamerlan was killed in April following a gun fight with police which ended when his younger brother ran him over while trying to escape.

Dzhokhar, recently brought to court, denied all changes. If convicted he faces life imprisonment or the death penalty.

MH