Eric Holder

This post was updated at 5:30 p.m. ET

Attorney General Eric Holder says "far more must be done to create enduring trust" between police and communities they serve, even as his Justice Department continues to investigate possible discriminatory police actions in Ferguson, Mo.

This post was last updated at 4:44 p.m. ET.

Eric Holder Jr., the nation's first black U.S. attorney general, will resign his post after a tumultuous tenure marked by civil rights advances, national security threats, reforms to the criminal justice system and 5 1/2 years of fights with Republicans in Congress.

The U.S. has devoted billions of dollars to fighting terrorism overseas in the years since the Sept. 11 attacks.

The Justice Department is increasingly warning about the danger posed by radicals on American soil, and U.S. Attorney General Eric Holder wants prosecutors and FBI agents to devote more attention to the threat.

Nearly two decades ago, after the Oklahoma City bombing killed 168 people, the Justice Department launched a group to fight domestic terrorism.