I've read a lot of speculation that the older brother was on track to being a contender, and bent it all up by becoming radicalized.
The younger brother has been described as a loser by his uncle, he may have just been a tag-along.
I think you have confused one detail. The older brother was described as a loser. Because of his domestic violence, he was denied citizenship and had a green card. The younger brother was affable and bright, and recently became a citizen. He was well liked and described as decent and modest. He had served as the captain of his high school wrestling team and a scholarship student at the University of Massachusetts at Dartmouth. The suspicion is that the younger brother was swayed by the elder. The elder had apparently been investigated by the FBI, but no action was taken, despite the fact that he had recently become ostensibly devout in his faith. He had upped youtube videos about how to pray more effectively.
I think more information will be forthcoming about Tamerlan (the elder) as this whole ugly business unfolds and more information is released. I suspect some stuff is held back because of the trial. It's early days, yet. The younger brother is still recovering in hospital and not communicating.
The sense portrayed in the press is that the older brother had trouble adjusting, had a chip on his shoulder, despite talent as a boxer. Sort of like he came here and got a chip on his shoulder and decided to don the fig leaf of religion in order to effect thuggery, dragging the younger brother along.
