By Scott Malone BOSTON (Reuters) - From the moment U.S. prosecutors stand up on Wednesday and begin their case against accused Boston Marathon bomber Dzhokhar Tsarnaev, their minds and those of their defense counterparts will be focused on just one thing: The death penalty. Tsarnaev, 21, is accused of killing three people and injuring 264 with a pair of homemade pressure-cooker bombs left at the race's crowded finish line on April 15, 2013, in the largest mass-casualty attack on U.S. soil since Sept. 11, 2001. "The bottom line is you're not going to get a not guilty in this case," said Jules Epstein, a Widener University School of Law professor who has represented defendants in federal and Pennsylvania death penalty cases. So every move is with an eye on the end game and that is avoiding death." Tsarnaev has pleaded not guilty to all charges and his attorneys have offered little detail on their case, with the bulk of both prosecution and defense filings under seal in Boston federal court.