This combination of undated photos shows Tamerlan Tsarnaev, 26, left, and Dzhokhar Tsarnaev, 19. (Photo: AP)
Boston Mayor Tom Menino says the information he has indicates that the suspects in the Boston Marathon bombing -- the brothers Tamerlan and Dzhokhar Tsarnaev -- acted alone.
"All of the information that I have they acted alone, these two individuals, the brothers," he remarked on ABC's This Week. "The older brother's dead now. We have the second one at Beth Israel Hospital in very serious condition, and we don't know if we'll ever be able to question the individual."
The mayor added that he believes the elder brother was really the ringleader in the plot.
"Yes, I think the older brother [Tamerlan] was really the leader, and the younger brother was, like you said, brainwashed by his brother, and he just was a follower," Menino said. "He followed his brother, the brother [read] those magazines that were published on how to create bombs, how to disrupt the general public, and things like that. And he brainwashed his younger brother..."
Yet many have their doubts, instead believing that the brothers may have been affiliated with a larger extremist network that provided guidance or training.
Fox News reports:
Investigators are exploring potential links between Boston Marathon bombing suspect Tamerlan Tsarnaev and an extremist group known as the Caucasus Emirate, sources tell Fox News.
The purported leader of the separatist and Islamic extremist group is Doku Umarov, a Chechen Islamic militant in Russia whose ordering of numerous attacks on civilians has earned him the nickname Russia's Usama bin Laden. The U.N.'s Al Qaeda sanctions committee has also cited Umarov for his alleged connections with Al Qaeda and other extremist groups.
The investigation is based on the contents of Tsarnaev's YouTube channel and his trip to Russia in the first half of 2012, which included stops in Dagestan and Chechnya.
Sources tell Fox that videos deleted from his YouTube account include a “terrorist playlist” and links to Vilayat Dagestan, which is associated with Caucasus Emirate.
A source said to be close to the investigation told the U.K. Mirror: “They were too advanced [to be acting alone]. Someone gave the brothers the skills and it is now our job to find out just who they were. Agents think the sleeper cell has up to a dozen members and has been waiting several years for their day to come.”
The Caucasus Emirate is apparently only one of several extremist groups being investigated, and it should be noted that an unnamed source told the Interfax news agency: "At the moment, we have no credible information about the Tsarnaev brothers' involvement with the Caucasus Emirate movement."
Governor Deval Patrick, speaking on “Face the Nation" Sunday, summarized: "There are lots of questions about how and why.”
Fox News has more on the story:The Associated Press contributed to this report.