Civil rights leader the Rev. Al Sharpton learned that his mother died Thursday, but he stuck to his planned appearance: leading a Florida rally for the slain unarmed black teen Trayvon Martin. The nation’s attention has turned to the town of Sanford since neighborhood-watch volunteer George Zimmerman shot the 17-year-old last month. The rally was originally planned for a local church but later changed to a park as attendance was expected to balloon. A grand jury will convene April 10 to review the case, which is also currently under investigation by the Department of Justice and the FBI.