Feb. 15 (UPI) -- A witness who saw a troubled former student step onto the grounds of Marjory Stoneman Douglas High School radioed a co-worker in alarm. Within a minute, he heard gunshots and called in a "code red" -- emergency on campus.
The witness, whose account is outlined in the arrest report for 19-year-old Nikolas Cruz, knew Cruz wasn't allowed on campus, the report indicates.
The witness -- whose name was redacted -- said he saw the suspect whom "he recognized as a former troubled student." Cruz arrived in a "small, goldish-colored vehicle" -- later revealed to be from Uber -- and carried a black duffel bag and wore a black backpack.
The witness "stated that he radioed his co-worker to alert him that Cruz was walking purposefully toward the 1200 building" of the school, the report states. "Within a minute, he heard gunshots and called a 'Code Red,' indicating an emergency on campus."
Cruz attended the Parkland, Fla., school but had been expelled for "disciplinary reasons," Broward Sheriff Scott Israel said after Wednesday's attack that killed 17 people.
Cruz appeared in Broward County Court on Thursday, where Judge Kim Theresa Mollica ordered him held without bond on 17 counts of premeditated murder.
The arrest report from Broward County Court said an Uber driver -- whose name was redacted -- told investigators she drove Cruz to the school and dropped him off there.
Cruz confessed to investigators that he brought an AR-15 to the school and began shooting students in the hallways and on the campus grounds, the report said. He hid additional magazines in his backpack.
As students began to flee the campus, Cruz planned to discard the rifle and magazines "so he could blend into the crowd."
Robert Lasky, the special agent in charge of the FBI's Miami office, said the bureau had been warned about a comment made on YouTube in September by a user with the name Nikolas Cruz.
"I'm going to be a professional school shooter," the comment said.
The FBI said it couldn't "positively identify" whether the YouTube comment came from the same man.
"No other information was included with that comment which would indicate a time, location or the true identity of the person who made the comment," Lasky said. "The FBI conducted database reviews, checks but was unable to further identify the person who actually made the comment."
The FBI has taken over as the lead investigative agency in the shooting.
At a news briefing Thursday, Israel said, "Law enforcement, the FBI and ourselves will do everything we can to make sure this person is convicted of all charges and that justice is served."
"Pathetic" copycat threats were also made at other schools, Israel said.
Florida Gov. Rick Scott said he planned to sit down with state leaders next week to ensure students are safe at school and that individuals with mental illness don't have access to guns.
"We want to make sure this never happens again." Scott said. "The violence has to stop. We cannot lose another child in this country to violence in a school.
"If someone is mentally ill, they can't have access to a gun."
President Donald Trump issued a presidential proclamation to honor the victims -- ordering all flags at the White House, public buildings nationwide and U.S. military installations around the world to be flown at half-staff until sunset Monday.
In a news conference, Trump said mental health needs to be a top priority for young students.
"No child no teacher should ever be in danger in an American school," Trump said. "No parent should ever have to fear for their sons and daughters when they kiss them goodbye in the morning.
"Answer hate with love and answer cruelty with kindness. Making our children safer will be our top priority."
Students described the chaos of the attack, saying the shooter walked the halls of the high school just before the end of classes Wednesday, carrying the assault rifle, after a fire alarm was activated. He wore a gas mask and lobbed smoke grenades as he went through the building.
Freshman Jason Menchaca told UPI he had tunnel vision running past the dead on the floor of his school as he escaped.
"It was just a normal good day so far and school was about to let out and I heard two shots, so we ran to the corner of the room and the fire alarm goes off right after that," Jason said. "I heard shot after shot, people screaming and running. I was scared for my life sitting in the corner praying for my life."
He said it took 45 minutes for authorities to free the students from the classroom -- shouting at them to run out as fast as they could.
"It was a terrible scene," Jason added. "I had none of my belongings so I just ran hoping that I could find my family."
Other students said they took cover beneath desks, hiding in closets for hours and barricading classroom doors to deter the shooter from entering.
"The people next door to us must have not locked their door," 14-year-old Hannah Siren said.
"I'm absolutely sick to my stomach to see children who go to school with backpacks and pencils lose their lives," Israel said.
Editor's note: An earlier version of this story included information from Sen. Bill Nelson, D-Fla., who told CNN and MSNBC on Feb. 14 that the shooter was wearing a gas mask and carrying smoke grenades. On Feb. 16, Broward County Sheriff Scott Israel said this information was incorrect. Police did find a balaclava at the scene, a ski mask with cutouts for the eyes.