According to police, Nikolas Cruz, 19, who is accused of killing 17 people at Marjory Stoneman Douglas High School in Parkland, Florida, on Wednesday, has confessed to the shooting.
In his statement to the court, Cruz said he arrived on campus with a rifle and extra ammunition in a black duffel bag and backpack, he began shooting students before discarded his weapon in an attempt to blend in with classmates. This allowed him to flee the scene undetected before entering a Walmart and then a McDonald's. He was spotted and arrested by the police in a nearby neighbourhood one hour after the attack.
This is the deadliest US school shooting since 2012 and he has appeared in court charged with 17 counts of premeditated murder.
The FBI has admitted it received a tip-off about him last year from YouTube user, Ben Bennight, who contacted the FBI and spoke to representatives for about 20 minutes after seeing a comment by Mr Cruz on a YouTube post.
According to the FBI, they were made aware of the comment and had conducted "checks" but were unable to identify the person behind it.
Mr Bennight said the FBI has been in contact with him again since this shooting.
Speaking to the Miami Herald, maths teacher, Jim Gard, said school authorities had emailed teachers about Mr Cruz's behavioural issues, "There were problems with him last year threatening students, and I guess he was asked to leave campus," he said.
Some students said they had joked "he's the one to shoot up the school". Speaking to Reuters, a former classmate, Chad Reuters, said Mr Cruz was an "outcast" who was "crazy about guns".
Broward County Sheriff, Scott Israel, said his social media profiles were "very, very disturbing," revealing his apparent interest in weapons, with two separate (now closed) Instagram accounts, showing Mr Cruz posing with guns and knives.
As details of the 17 victims emerge, so do the stories of bravery.
The school's assistant football coach, Aaron Feis, jumping in front of students to shield them from bullets. He was taken to hospital but succumbed to his wounds. An emotional tweet from his team read; "It is with Great sadness that our Football Family has learned about the death of Aaron Feis. He was our Assistant Football Coach and security guard. He selflessly shielded students from the shooter when he was shot. He died a hero and he will forever be in our hearts and memories"
The Athletic Director, Chris Hixon, 49, who served as a US Naval Reservist in Iraq in 2007, was also confirmed dead by local media.
Student, Kelsey Friend, said her geography teacher, Scott Beigel, died while trying to lock the door of the classroom, but was just too late.
The student victims identified so far are:
Alaina Petty, 14
Alex Schachter, 14
Martin Duque, 14
Gina Montalto, 14
Jaime Guttenberg, 14
Luke Hoyer, 15
Alyssa Alhadeff, 15
Carmen Schentrup, 16
Joaquin Oliver, 17
Nicholas Dworet, 18
Meadow Pollack, 18
On Thursday, speakers demanded tougher gun laws as thousands of people chanting "no more guns" attended a candlelit vigil to honour the victims.
As is always the case, the conversation soon turned to gun control. Florida's Democratic Senator, Bill Nelson, asked what it would take "for enough to be enough" while Florida's Republican Senator, Marco Rubio, said that it was too soon to debate whether tighter gun laws could have stopped it.
Democrats were accused of politicising the shooting by Texas Senator, Ted Cruz, saying to Fox News: "They immediately start calling that we've got to take away the Second Amendment rights of law-abiding citizens. That's not the right answer".
During a CNN interview, an emotional mother of one of the victims called on President Trump to respond with policy.
"Do something. Action, we need it now. These kids need safety now," she said.
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