While legal experts said the federal government is extremely unlikely to bring civil rights charges against Zimmerman, the report will examine the circumstances before the Florida neighborhood watch captain fatally shot Martin, an unarmed black teenager, inside a gated community.
The Washington Post reported Tuesday Holder promised the full report on the department's investigation, launched shortly after the 2012 killing, will be completed "relatively soon."
Experts said civil rights charges are unlikely to be filed because they would be almost impossible to prove in the case. Zimmerman's acquittal on second-degree murder charges in state court further complicate a potential federal case.
In federal civil rights cases, prosecutors would have to prove beyond reasonable doubt not just that Zimmerman intended to kill Martin but the motive was his race.