Five former police officers were charged this week with second-degree murder in Nichols' death.
Wray spoke alongside U.S. Attorney General Merrick Garland, who said he had not seen the footage but told reporters, "it is deeply disturbing, let me say, horrific, from the descriptions I've been given."
Footage of the encounter is scheduled to be released Friday evening.
Instances of police brutality toward Black Americans have in the past sparked demonstrations and outrage that have on occasion resulted in instances of vandalism and looting.
Wray, along with U.S. Attorney General Merrick Garland, urged a peaceful and nonviolent response when the video of Nichols, who later died from his injuries, is made public.
