Trayvon Martin timeline: Key events in the Sanford, Fla., shooting case Mary Altaffer / AP Demonstrators pray during the Million Hoodie March in Union Square Wednesday, March 21, 2012 in New York. The march was in memory of Trayvon Martin, an unarmed teen shot and killed in Florida in February. Feb. 26, 2012: Fatal Shooting Trayvon Martin, 17, is shot and killed while walking through a Sanford, Fla., community where he is visiting family. Neighbors call police to report hearing a scuffle and a gunshot. Martin is found dead by police. George Zimmerman, neighborhood watch captain, is taken to the Sanford Police Department for questioning about the shooting, which he says was in self-defense. No charges are filed and he is not arrested. March 16: 911 tapes released Martin's parents gain access to 911 calls made to police on the evening of the shooting and portions of those tapes are made public. One recording indicates that Zimmerman says he is following Martin and a dispatcher tells him that's not necessary. In another, there are audible cries for help in the background. Martin's family demands an arrest and petitions calling for the same gain tens of thousands of signatures within a matter of hours. March 19: Investigation launched The U.S. Justice Department announces it has launched an investigation into the shooting. March 21: Million hoodie march Martin's parents join hundreds of protesters in New York City demanding justice in what is dubbed the "Million Hoodie March," a tribute to Martin, who was wearing a hooded sweatshirt at the time of his death. It is the first of what will become large protests across the country. March 22: Police chief steps aside Sanford Police Chief Bill Lee announces he will step down "temporarily" amid accusations that he has mishandled the Martin case and after a vote of no confidence by city commissioners. Thousands of people join a rally in Sanford organized by the Rev. Al Sharpton demanding Zimmerman's arrest. Sharpton is a host on the msnbc cable television show Politics Nation. March 23: White House mention President Barack Obama raises the Martin case at the end of a White House press conference in which he names Jim Yong Kim as his nominee for the World Bank president. In response to a reporter's question about the case, Obama says: "If I had a son, he would look like Trayvon." March 24: Threats against Zimmerman At a protest in Florida, leader of the New Black Panther Party Mikhail Muhammad announces a $10,000 bounty for the capture of Zimmerman, who is in hiding. April 10: Lawyers quit Craig Sonner and Hal Uhrig, lawyers for Zimmerman, announce they will no longer represent him because he has stopped communicating with them. April 11: Charges pending A law enforcement official tells NBC News that the Florida prosecutor will file criminal charges against Zimmerman.