On Valentine's Day in 2018, Nikolas Cruz walked through the doors of his former high school with a backpack stuffed with an AR-15-style rifle and magazines.
That afternoon, the 19-year-old took an Uber to Marjory Stoneman Douglas High School, the school he had been expelled from a year earlier.
Inside the school, Cruz began loading the rifle when a student walked past him in the east stairwell.
"You better get out of here," Cruz told him. "Something bad is about to happen."
Cruz then began wandering down the halls of the school firing indiscriminately at students and staff, just minutes before the end of the school day.
The smoke from his rifle set off the fire alarm while bullets shattered windows. Students ran for their lives or hid in classrooms and bathrooms.
The attack lasted seven minutes and would become known as one of the deadliest school shootings in the US, killing 17 and injuring more than 15 others.
Cruz, who had a history of mental health and behavioural issues, was later apprehended by police shortly after leaving the school.
A YouTube comment and mobile phone videos.
A day after the mass shooting, the FBI confirmed they were warned of an ominous message left on a YouTube video by someone with the username "nikolas cruz".
"I’m going to be a professional school shooter," it read.
The comment was noticed by YouTube vlogger, Ben Bennight, who alerted authorities and flagged it with YouTube.
After the shooting, FBI Special Agent Rob Laskey told a press conference that "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 also recorded three videos on his mobile phone discussing his plans in the lead up to the shooting.
"When you see me on the news, you’ll all know who I am," he said in one video. "You’re all going to die."
Cruz pleads guilty.
Three years later, Nikolas Cruz has now pleaded guilty to 17 counts of murder and 17 counts of attempted murder that occurred on that fateful February day.
A penalty trial with 12 jurors will now decide whether he should be sentenced to death or life in prison without parole.
Following the plea, the 23-year-old apologised to the victims' families, some of whom broke down in tears while listening to the court proceedings via a video conference.