Martin Richard

A poignant photo posted on Facebook Tuesday showed Martin Richard, the 8-year-old victim in the Boston Marathon bombings, calling for an end to violence.

A friend of Martin's teacher Rachel Moo uploaded a photo of him holding up a sign that reads: "No more hurting people. Peace."

Obama: Boston Marathon bombings an "act of terror"; no suspect in custody

"His message resonates powerfully today," Lucia Brawley wrote. "My prayer is that we all live by Martin's words, paying tribute to his too-brief, but immeasurably valuable life by following his example."

The poster was made last May for Moo's second-grade class peace march, which was organized following the Trayvon Martin shooting.

Martin was one of three people killed Monday in the bombings. He and his family were waiting for his father, Bill, at the finish line of the marathon. Both his mother and younger sister were critically injured as well.

"My dear son Martin has died from injuries sustained in the attack on Boston," Bill Richard said in a statement Tuesday, obtained by People. "My wife and daughter are both recovering from serious injuries. We thank our family and friends, those we know and those we have never met, for their thoughts and prayers. I ask that you continue to pray for my family as we remember Martin. We also ask for your patience and for privacy as we work to simultaneously grieve and recover. Thank you."

On Tuesday, a second victim was identified as 29-year-old Krystle Campbell. Her father, William A. Campbell Jr., told Yahoo! News that his daughter was at the finish line with a friend, Karen Rand, to cheer on her boyfriend.

"My daughter was the most lovable girl. She helped everybody, and I'm just so shocked right now. We're just devastated," he said. "She was a wonderful, wonderful girl. Always willing to lend a hand."