By John Blake, CNN

(CNN) - An angry outburst at a mosque. The posting of a suspicious YouTube video. A friendship with a shadowy imam.

Those were just some of the signs that Tamerlan Tsarnaev, accused of masterminding the Boston Marathon bombings, had adopted a virulent strain of Islam that led to the deaths of four people and injury of more than 260.

But how else can you tell that someone’s religious beliefs have crossed the line? The answer may not be as simple you think, according to scholars who study all brands of religious extremism. The line between good and evil religion is thin, they say, and it’s easy to make self-righteous assumptions.

“When it’s something we like, we say it’s commitment to an idea; when it’s something we don’t like, we say it’s blind obedience,” said Douglas Jacobsen, a theology professor at Messiah College in Pennsylvania.

FULL POST