On Wednesday, February 2018, 19 year-old Nikolas Cruz entered Marjory Stoneman High School in Parkfield, Florida and pulled the fire alarm. Confused students and teachers began to file out into the hallways, where Cruz then began firing shots. He fired shot after shot outside and then followed others running back inside the building, where people who’d heard the shots were taking shelter, officials said.

There, he roamed the halls he knew so well, allegedly targeting those huddled in classrooms and then blending in with the students and staff evacuating the school. He was arrested in the neighboring community of Coral Springs later in the day, the Broward County Sheriff’s Office said.

While the reasons of this massacre are still unknown, chilling clues of what was going on before this tragedy took place are shedding a bit of light on the troubled teen’s motives.

First, Cruz was known to sharing pictures and comments on social media about weapons and guns. Julien Decoste, also a senior, said Cruz sometimes posted pictures on his Instagram feed of “dead lizards and stuff that he shot.” That Instagram page also has pictures of a figure, face obscured by bandannas and holding knives. Another shows a young man, presumably Cruz, holding a pistol, although it’s not clear whether the gun is real.

Chief Scott Israel of Broward County said investigators were reviewing social media postings that he described as “very disturbing.”

Classmate Eddie Bonilla said he knew Cruz before he got kicked out of school. “He got kicked out of school last year,” said Bonilla. “He always had guns on him and stuff like that.”

Mr. Israel later added: “What about the rights of people who go to school with book bags – don’t they have the right to be protected?” He also called people in the community “our eyes and ears” and said “right now, if you know anybody, this raises a red flag, don’t just think about calling us, call us.

Bonilla said he was not surprised by the arrest. “Honestly a lot of people a lot of people were saying it was going to be him,” Bonilla said. “We actually, a lot of kids threw jokes around like that, saying that he’s the one to shoot up the school, but it turns out everyone predicted it. It’s crazy.”

While many people did know of Cruz’s disturbing social media posts, it is still insane that people didn’t say anything to the police or administration.

School Superintendent Robert Runcie said there were no warnings that something like this would happen. “We received no warnings,” Runcie told reporters outside the school. “Potentially there could have been signs out there. But we didn’t have any warning or phone calls or threats that were made.”

On September 24, 2017, Ben Bennight, a bail bondsman at AFAB Bail Bonds in D’Iberville, Miss., saw a message on his YouTube channel “BenTheBondsman” from a commenter identifying himself as “nikolas cruz” that read:

“Im going to be a professional school shooter”

Bennight emailed a screenshot of the comment to the FBI.

On January 5, 2018, an anonymous person called the FBI’s Public Access Line, located in Clarksburg, W.Va., to warn about Cruz. The person cited concerns about:

“Cruz’s gun ownership, desire to kill people, erratic behavior, and disturbing social media posts, as well as the potential of him conducting a school shooting.”

The FBI said it did not follow established protocols to follow up.

“Under established protocols, the information provided by the caller should have been assessed as a potential threat to life,” the FBI said.

If you see something that is related to using weapons to harm others, please report it to your local police. It might be just a fluke, or it could save lives.

Social media can be a great tool to share pictures and videos with friends, but it can also be used to find those with malicious intents. Students that had social media accounts saw and witnessed Cruz’s posts and threats. Why didn’t they report Cruz? If the police had multiple records of Cruz’s actions, would they have been able to stop him from buying the weapon that took so many lives? People need to step up and make a change.

Just alerting the authorities can be enough, but also inform your school teachers and administration so some of the issues can be addressed at school. We, as a world, need to start calling people out when you feel like someone is in danger.

One could say that in the case of Cruz that the FBI was warned of him, or that the authorities were alerted. However, there were multiple times where someone saw something and didn’t say something, and this lead to this tragedy.