While this has nothing to do with guilt, it could damage the Government's credibility in the penalty phase, where it will dispute Jahar was overly influenced by his brother. In contrast, the defense gained credibility from the moment it began its opening, by admitting Jahar's participation in the bombing.

Brick by brick, the defense is telling its story to support its theme. The agent's testimony highlights for the jury just what the defense said in opening: Jahar was mostly focused on typical teen things like girls, cars, food, sleep, and homework, who became radicalized by his brother. That's the theme of the defense. As you follow the trial, try to follow the story the defense is telling in support of its theme. Everything they do is intended to advance their theme. If a Government witness' testimony doesn't detract from their theme, and is unlikely on cross examination to further it, they don't cross-examine at all.

Yesterday, the prosecution played videos of the Tsarnaev brothers at the scene of the Boston Bombing. In almost all the ones I saw of them together, Jahar is following behind Tamerlan. (A few had them side by side, but I didn't see any with Tamerlan following Jahar.)