http://edition.cnn.com/2012/03/23/justice/florida-teen-shooting/index.html?hpt=hp_t1 Sanford, Florida (CNN) -- President Barack Obama waded into the growing national controversy of the killing of an unarmed black teenager in Florida, saying the nation should do some "soul-searching to figure out how something like this happens." "I think every parent in America should be able to understand why it is absolutely imperative that we investigate every aspect of this and that everybody pulls together, federal state and local, to figure out exactly how this tragedy happened." Obama said Trayvon Martin's death particularly resonated with him as an African-American parent. "If I had a son, he'd look like Trayvon," Obama said in brief remarks outside the White House. As Obama was speaking, demonstrators were preparing to march to the state capitol in Tallahassee, Florida on Friday to protest the death of the17-year-old, who was shot and killed by a neighborhood watch volunteer while walking home from a convenience store. The death has sparked outrage nationwide. More than 1.3 million people have signed an online petition urging authorities to file criminal charges against George Zimmerman, the neighborhood watch leader who has told police he shot Martin in self defense.