Thousands of people have rallied in Sanford, Florida for justice in the February shooting death of 17-year-old Trayvon Martin.

Human rights activists and others called for the immediate arrest of George Zimmerman, the man who admitted to shooting Martin but has not been arrested due to claims of self defense. Martin, who is African-American, was walking back from a convenience store when he and Zimmerman got into an altercation.

As the Martin case gains wider attention across the U.S., more than two million people have signed petitions on the social activist Web site “change.org,” calling on the court to seek justice.