MIAMI -

Protesters gathered outside the Seminole County criminal courts building Monday to call for the arrest of George Zimmerman. 

The 28-year-old neighborhood watchman is at the center of a controversy after police said he shot and killed an unarmed black teen last month. 

Trayvon Martin, 17, died steps from his stepmother's home after leaving a convenience store. 

Martin, a junior at Michael Krop Senior High School, was visiting his family. 

Zimmerman is claiming self-defense, and police said witness accounts and other evidence back up his claim. 

Martin's mother, Sybrina Fulton, however, still wants to see justice. 

"I just don't understand why somebody can just take his life," said Fulton. 

911 tapes released last week have raised further questions over the shooting. Experts who have listened to the tape said Zimmerman appears to have slurred some words and may have been under the influence. 

"I don't even think he would have been followed if he was a white kid," said Martin's father. 

Family and friends are asking the FBI to open an investigation. Meanwhile, the Rev. Al Sharpton is planning a March for Martin on Thursday.