FBI begins "parallel investigation" into Trayvon Martin shooting

(CBS/AP) - The FBI has begun its own investigation into the shooting of Fla. teen Trayvon Martin by neighborhood watch captain George Zimmerman, who claims he acted in self defense.

According to NBC, agents were questioning potential witnesses on Monday as part of a "parallel investigation" to determine if Martin's civil rights were violated.

An FBI official tells NBC that the bureau is investigating Zimmerman's background in order to determine whether he was racially motivated to pursue the unarmed 17-year-old after calling 911 to report Martin as 'suspicious.'

Zimmerman told police that he was attacked by Martin on Feb. 26 and believed he had no choice but to fire his gun at Martin in self-defense. The teenager's family believes Zimmerman, 28, singled Martin out as suspicious because he was black. Zimmerman's father is white and his mother is Hispanic.

Zimmerman's lawyer, Craig Sonner, denies that his client is racist. "This was not a case of racial profiling," he told NBC News on Sunday.

Complete coverage of the Trayvon Martin case on CBS News