FBI Director Christopher Wray said that they are "still investigating the facts," adding that the agency's officials have spoken with victims and families, and "deeply regret the additional pain this causes all those affected by this horrific tragedy."

The two statements came two days after Cruz opened fire on Wednesday with an AR-15 rifle at students and teachers at Marjory Stoneman Douglas High School in the city of Parkland in Broward County, just north of Miami on the state's southeastern tip.

Besides the 17 killings, the shooting also injured 14 others.

Cruz, who was expelled from the school for disciplinary reasons, made a brief court appearance on Thursday and was ordered held without bond.

Attorney General Jeff Sessions said Friday that he has ordered an immediate review of the processes at the Department of Justice and the FBI.

"It is now clear that the warning signs were there and tips to the FBI were missed," Sessions said in a statement. "We see the tragic consequences of those failure."

Wednesday's massacre also raised concerns about potential failure in school security and sparks ongoing U.S. debates on gun control.

During a national address on Thursday, President Donald Trump stressed safer schools for students and promised to tackle the "difficult issue of mental health" but did not mention the prevalence of guns or gun violence.

The president was expected to meet with those affected by the shooting in Parkland later Friday.