Today marks the first anniversary of the death of unarmed African-American teenager Trayvon Martin. On February 26, 2012, the 17-year-old high school junior was shot dead in Sanford, Florida, by George Zimmerman, a self-appointed neighborhood watch volunteer who claimed he was acting in self-defense. Police initially refused to arrest Zimmerman, but he was finally charged with second-degree murder after a wave of protests around the country. His trial is set for June.