article_snippet.sent: Heroic: Jeff Bauman can be seen running at the side of Jeff Bauman, who lost both legs in the 2013 explosion .
article_snippet.sent: Chilling: Martin Richard, who was killed in the bombings, is seen (front circle) just meters away from Tsarnaev (back circle) on April 15.
article_snippet.sent: Seconds later, one of two bombs exploded, piercing him body with shrapnel .
article_snippet.sent: Krystle Campbell (left) and Martin Richard (right) were killed in the blast at the marathon finish line .
article_snippet.sent: Killed: Lingzi Lu, 23, also died at Boston Marathon, while MIT Police Officer Sean Collier, right, was later shot dead .