Thousands rally in Miami with parents of Trayvon Martin

The parents of slain teen Trayvon Martin returned to Florida from Washington, D.C., on Sunday to take part in a homecoming rally, and will ask the U.S. Justice Department to investigate local authorities they believe interfered with the case, their attorney said.

The Justice Department's civil rights division had already agreed to review the local Florida investigation into the racially charged case that has riveted the country.

Waves of demonstrations have called for the arrest of George Zimmerman, 28, who said he shot Martin in self-defense on Feb. 26.

"We need to stand up for Trayvon," Florida state Rep. Frederica Wilson (D-Miami) told reporters at Sunday's rally in Miami, according to the Miami Herald.

Martin, a black 17-year-old, was unarmed and walking through a gated community in Sanford, Fla., when Zimmerman mistook him for a would-be burglar. Zimmerman, who is half white and half Hispanic, told police that Martin attacked him first.

Meanwhile, screams heard on a 911 audio call during the incident don't appear to be Zimmerman, the Orlando Sentinel reported Saturday.

A forensics consultant told the newspaper there's "reasonable scientific certainty" it wasn't Zimmerman, although there was also no sample of Martin's voice to conclude it was him either.

Initially, a Sanford police detective unconvinced by Zimmerman's story of self-defense wanted to charge him with manslaughter, but was overruled by a local state attorney. Martin's family wants answers why, their lawyer said.

(With Reuters)