He will be held without bond on 17 counts of premeditated murder.
On the 19-year-old's back: A pack full of magazines loaded with bullets.
The suspected shooter in the Parkland, Florida, massacre had ties to a white supremacist group, according to the Anti-Defamation League (ADL).
The group wants Florida to become its own white ethno-state.
Nations said sometimes it's hard to track usernames and there are Constitutional laws investigators have to abide by.
"President trump, you say what can you do?" But we are not powerless. "Caring for our kids is our first job". "We all got on the floor and under the desk", said Rebecca, who was still shaking outside the school.
The username was the same as the Florida school shooting suspect.
He pushed to tighten access to firearms but was blocked by the Republican-controlled Congress.
He had been a member of the Junior Reserve Officers' Training Corps, a government high school program that provides preparatory training for the military, including marksmanship. "Please, this is the 18th [shooting] this year - that's unacceptable".
Lori Alhadeff, the mother of a 15-year-old victim of the Parkland school shooting, voiced her frustration during an interview on Thursday.More news: Moto G6 release date, price, news and rumours
Postings under the name Nikolas Cruz included threatening comments under videos on YouTube and other sites, including "I whana shoot people with my AR-15" (sic), "I wanna die Fighting killing s**t ton of people" and "I am going to kill law enforcement one day they go after the good people".
"The FBI conducted database reviews, checks, but was unable to further identify the person who actually made the comment", said FBI Special Agent in Charge Rob Lasky.
Ben Bennight, from MS, has claimed in a video posted on the channel that he flagged up a suspicious phrase left by a user named "nikolas kruz" last September.
"I knew that I couldn't just ignore that", Bennight said.
Bennight said he reported it to YouTube and the Federal Bureau of Investigation, who interviewed him the next morning and again visited him after the shooting on Wednesday.
"We have our anonymous emergency system that everyone can report to, in addition adults in our building, our teachers, our security officers, our administrators, any situation that may arise on the campuses, they can report to them".
"He told me how he got kicked out of two private schools".
He crossed fields and ran west along with others who were fleeing.
Cruz, an orphan, had been living with family friends at the time of the shooting.
Nikolas Cruz, 19, remained silent as he stood in front of a Broward County judge.
"His mother had died back in November of past year, and this family took him in", Lewis told the news station.
Unhappy there, Nikolas Cruz asked to move in with a friend's family in northwest Broward County. "This is not fair to our family, that our children go to school and have to get killed". He did have the key, however.