Holder Appeals for Peace Ahead of Ferguson Decision

While a Missouri grand jury secretly decides whether to charge Ferguson police officer Darren Wilson for fatally shooting Michael Brown, the nation's top law enforcement official today called on concerned Americans to appreciate "the gravity" of the matter and express themselves peacefully.

"History has ... shown us that the most successful and enduring movements for change are those that adhere to non-aggression and nonviolence," Attorney General Eric Holder said in a video released by the Justice Department.

The message comes just days after the FBI -- an agency overseen by Holder -- warned law enforcement agencies across the country that extremist, violent protesters could hijack otherwise peaceful demonstrations nationwide. And it comes one day after Brown's own father issued his own call for calm.

"Hurting others or destroying property is not the answer," Michael Brown Sr. said in a public service announcement. "No matter what the grand jury decides, I don't want my son's death to be in vain."

Holder echoed that sentiment in his message today, saying recent protests have highlighted "real and significant underlying issues involving police practices, implicit bias, and pervasive community distrust."

Brown Sr. said he hopes the recent controversy will spark "incredible" and "positive change," particularly over how police forces interact with the citizens they vow to protect.

In fact, the Justice Department is not only weighing whether to file federal criminal charges against Wilson himself, but it is also conducting a separate civil probe into the entire Ferguson police department, trying to determine whether officers routinely engage in a "pattern or practice" of unlawful and discriminatory policing.

In August, when pressed by ABC News, Holder seemed to acknowledge federal charges against Wilson are hardly guaranteed. And current and former officials have outlined several challenges associated with building such a case.

Nevertheless, Holder today noted that "long-simmering tensions will not be cooled overnight," and he touted the "importance" of police forces engaging with communities long before times of crisis.

Holder suggested police officials discuss with citizens even seemingly minor issues such as what uniforms officers should wear.

"[This] hard work ... is necessary to preserve the peace and maintain the public trust at all times - particularly in moments of heightened community tension," he said.

Law enforcement officials contacted over recent days by ABC News - stretching from Los Angeles to the Atlanta area - remained confident that such work would help maintain peaceful protests in their cities after the Ferguson decision is announced.

In Indianapolis, for example, police have held two town-hall meetings in the past two months to discuss the Ferguson issue with concerned residents and build a "bank of trust," Rick Hite, the chief of the Indianapolis Metropolitan police department, told ABC News.

Still, federal authorities are urging vigilance.

"The announcement of the grand jury's decision ... will likely be exploited by some individuals to justify threats and attacks against law enforcement and critical infrastructure," the FBI said last week in its intelligence bulletin, first obtained and reported by ABC News.

In his video message, Holder commended law enforcement for its response so far to Ferguson-related demonstrations across the country, saying "the vast majority of law enforcement officers have honorably defended their fellow citizens engaged in these peaceful protests."

Holder also announced that the Justice Department was issuing new guidance to federal, state and local law enforcement agencies "about how to approach maintaining order during First Amendment-protected events."

The guidance includes information and "best practices" that "will help law enforcement officers maintain public safety while safeguarding constitutional rights," Holder said.