Other statements by Meng that may help the defense in the penalty phase: Tamerlan admitted to Meng that he (as opposed to "we")just killed a police officer.

Meng said Tsarnaev asked him if he knew who committed the Boston Marathon bombing.

"He said, 'I did it, and I just killed a policeman in Cambridge,'" Meng said.

When the defense doesn't cross examine a witness, it's because doing so is unlikely to advance its theme that Jahar was a typical teen until he fell under the influence of his brother. The theme was introduced in the defense opening. "It was Tamerlan who self-radicalized,” Clarke said. “It was Dzhokhar who followed.” It will argue his lack of a leadership role, his youth, his troubled family life and history, and his lack of prior serious criminal activity are all mitigating factors warranting a life sentence.

I think Mung helped further the defense theme today. Of course, it remains to be seen whether any juror will be persuaded, given the extensive testimony about injuries and photos of the carnage already introduced, and which they will see and hear more of in the sentencing phase.