there could be some reasonable doubt lingering. >> hernandez's former legal trouble were not allowed into this court case. >> very significant. i think the motivation would have been is hernandez was killing him in order to keep him from talking about past crimes. the judge kept that out. >> let's talk about the penalty phase for the boston marathon bomber dzhokhar tsarnaev the 21st of april, what's the defense have to do? >> the prosecution has to present evidence of so-called aggravating factors. particular circumstances to be proven beyond a reasonable doubt that show that he should die for what he did. so, for example, special cruelty or premeditation. in human terms, the prosecution is focusing on the victim impact. people will talk about the heartbreaking impact it had on them and the utter lack of remorse on the part of tsarnaev. >> defense has to do what? >> defense has uphill battle but what they have to do is humanize somebody who's been