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PARKLAND (CBSMiami) – Wednesday could best be described by words like “shock” and “disbelief” after it was revealed that 17 people had been killed at Marjory Stoneman Douglas High School by a lone wolf gunman.

Thursday, the realization began to creep.

Nikolas Cruz, 19, was denied bond during his first court appearance. He is accused of carrying out the premeditated and sustained assault on the students, teachers, and staff with his rifle – an AR-15.

An arrest report says Cruz confessed to carrying out a planned and violent attack at his former school.

“Cruz stated that he was the gunman who entered the school campus armed with an AR-15 and began shooting students that he saw in the hallways and on the school grounds. Cruz stated that he brought additional loaded magazines to the school campus and kept them hidden in the back pack until he got on campus to begin his assault.”

Timeline: The Events Before, During & After The Florida School Shooting

After the shooting…”as students began to flee the campus on foot he decided a plan to discard the AR15 and vest with the additional magazines so he could blend into the crowd.”

The Bureau of Alcohol, Tobacco, Firearms, and Explosives determined that Cruz bought the gun in February 2017 from a local gun store.

Fellow students say Cruz was troubled and often talked about violence and guns. He was expelled from Stoneman Douglas last year but a specific reason for the expulsion has not been given.

“It is a student that we’ve been providing support for. There certainly were challenges,” said Broward Schools Superintendent Robert Runcie.

Reports emerged also that the FBI got a tip last year that a person named Nikolas Cruz posted a comment on YouTube about being a professional school shooter. The FBI addressed that Thursday.

“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.

The tip to the FBI came from a blogger in Mississippi who noticed the alarming comment on a video he’d posted back in September 2017.

“Im going to be a professional school shooter,” read the comment, left by a user with the name Nikolas Cruz. According to the FBI, when the blogger notified YouTube, it removed the comment.

Agent Lasky reiterated at a Thursday afternoon news conference, “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.”

Cruz arrived at his old school around dismissal time, when things are more open on campus. He was brought to the school in an Uber.

A source confirmed that he arrived with extra clothes and a rifle in a duffel bag.

An employee at the school saw him and knowing that Cruz was a troubled young man he radioed to a co-worker.

But it was too late as the shooting had already started.

According to a source, CBS4 has learned that all the deaths inside the school occurred on the first floor.

In many cases, the source explained, the victims in many cases fled to a corner of a room and crouched down, making them easy targets for the gunman.

Eventually, Cruz went to the third floor teachers’ lounge.  The source says Cruz attempted to shoot out the window at students that were fleeing from the school on the football field.

Fortunately, the glass was impact resistant which prevented this from happening.

At that point, the source explained, Cruz gave up and changed his clothes in order to blend in with other fleeing students.

He was picked up about a mile away by a Coconut Creek officer.

Broward Sheriff Scott Israel confirmed there was an armed school resource officer on campus at the time of the shooting, but he never encountered Cruz.

In the wake of this tragedy, the conversation has turned to gun control and limiting access of people with mental health issues to firearms. Governor Rick Scott said that’s a conversation that needs to had.

“How do we make sure that individuals with mental illness do not touch a gun. We need to have a real conversation so we have public safety for our schools in this state,” said Scott.

School leaders say these scenes have prompted students to demand something be done. Students say they felt let down by the adults running the school system.

“We’ve got to invest resources to make sure this doesn’t happen again, because if we don’t, it won’t be a question of if, it will be when,” said Scott.

The Broward Sheriff’s Office and FBI have said they want to hear from people who have information about the shooting. There is a tipline that’s been established at