"Bartick was confident that he had a better than evens chance of persuading the jury of Paul's redeeming characteristics--in the event that he was found guilty of murder" (Weinberg, 236).
I didn't realize death sentences were given a separate trial from the original murder trials. This explains why character references may play such a strong part in the sentences. California has not sentenced a prisoner to execution since 2006 so the laws have changed since this trial. However, in 2003 the New York Times wrote an article about jurors sparing the lives of prisoners in exchange for life without parole. The article claims one of the main contributors to this change was an increase in defense attorneys convincing jurors the lives of their clients are worth saving. This is definitely what Bartick was planning to do with Frediani if he was found guilty of murder.