BOSTON—Just 3 miles from the spot where twin bombs exploded here in 2013, killing three people and wounding hundreds, alleged attacker Dzhokhar Tsarnaev is set to go on trial this week in a case expected to hinge on dueling portraits of the former college student.

Federal prosecutors likely will seek to show Mr. Tsarnaev as a remorseless architect of the explosions at the Boston Marathon, one who bantered with friends and went to the gym in the days after the attack, even as a shattered city mourned victims who included an...