If you or someone reading this doesn't know who or what this case is about:
Emmett Till was an African American boy around 16 when he "whistled" at a white woman. This was in the mid-late 1900s I believe. The family of the white woman didn't like the way a black man had treated their white daughter/sister/whatever relationship. They killed him for what he'd done. If you have the stomach, look up "Emmett Till's body" on Google images. It's disgusting. He was beaten, shot, burned, and more.
People protested Emmett's death because he and his family deserved justice for what had been done. This was an act of racism. The also protested the death because the 2 men who'd killed him hadn't received any punishment for their tourture of Emmett Till.
Hoped this helped :)