will be sentenced to life in prison or 25 years. arias always admitted to killing alexander, but she always maintained that it was in self-defense. heart wrenching testimony from survivors of the boston marathon bombings on the second day of the trial of accused bomber dzhokhar tsarnaev. one victim described it as "pure carnage." another took the stand to recount the moment she lost her leg. >> reporter: 12 seconds after the first bomb exploded, the second bomb and a backpack carried by dzhokhar tsarnaev detonated. initially, the crowd, having heard the first blast, can be seen turning to look at the finish line. images show spectators standing one moment, seconds later, flattened on the sidewalk. bill richard and wife denise were outside the restaurant watching the race with their three kids.