A BBC news program reports that Tamerlan Tsarnaev was heavy into "right-wing literature" and owned reading material about mass killings, conspiracy theories, and white supremacist rantings. The show, Panorama, spoke to friends of the bombers to try to paint a portrait of their lives and motivations, and found that the older, now deceased brother, appeared to take interest in ideas that went far beyond just the typical jihadist propaganda.
Their investigation also seems to fit with a similar portrait of Tamerlan that emerged in Janet Reitman's Rolling Stone cover story about his brother, Dzhokhar. The older brother was described as a more devout Muslim, who spent most his free time reading Islamic websites, but was also allegedly a fan of InfoWars, the site run by radio host Alex Jones, who has implied that the Boston bombing was a "false flag." (InfoWars is already pushing back on the story.)
Obviously, owning reading material doesn't mean that one endorses everything that's written in it. Though it does appear there is a strong anti-government streak running through his choice of reading. One of the pieces was apparently about "the rape of our gun rights," while another espoused that "Hitler had a point." The white supremacist literature is more problematic, since Tsarnaev, a Muslim from a foreign country, would probably not be welcome in that movement. (Even if he is from the actual Caucasia.) However, the same anti-government, anti-Semitic thread runs through much of that writing as well.
Perhaps the most disturbing part is that he read up on mass killings and how the perpetrators carried out their crimes calmly. The wide-range of materials that he seemed interested might even suggest that, rather that someone who was "radicalized" by militant Islamist ideas, Tamerlan Tsarnaev may have been a disturbed and violent individual, who merely found jihad as an excuse for his behavior.
You can see clips from the Panorama broadcast on the BBC website.