The suspect in the Florida high school shooting that killed 17 has confessed, police said Thursday.

Nikolas Cruz, 19, told police he was responsible for the shooting and added that he hid extra ammunition in his backpack and shot students in the hallways and on school grounds, Broward County Sheriff Scott Israel said.

Israel also revealed Cruz’s bizarre movements in the hour after he allegedly opened fire at Marjory Stoneman Douglas High School, killing 17 and wounding others.

Cruz arrived at the school by taking an Uber car, took the rifle out of a case and began shooting in classrooms, Israel said. He then dropped the AR-15 assault rifle he used and his vest to blend in with students. Cruz then left the school and ran along with other students fleeing to blend in.

He then went to a Walmart, bought a drink in a Subway, left and then went to a McDonald’s. After walking out of the McDonald’s he was taken into police custody without incident.

The news comes after the FBI confirmed agents were warned five months ago about a YouTube comment that may have come from Cruz.

Parents wait for news after a reports of a shooting at Marjory Stoneman Douglas High School in Parkland, Fla., on Feb. 14, 2018. Joel Auerbach—AP

“In 2017, the FBI received information about a comment made on a YouTube channel. The comment simply said, ‘I’m going to be a professional school shooter.’ 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. The FBI conducted database reviews, checks, but was unable to further identify the person who actually made the comment,” FBI Special Agent Rob Lasky said during a press conference.

The username on the comment was “nikolas cruz.”

Broward County Sheriff Scott Israel also said that over the past few years his office had received about 20 calls for service regarding Cruz and his younger brother, and that each one would be “looked at and scrutinized.”

Cruz is charged with murdering 17 people at Marjory Stoneman Douglas High School in Parkland, Florida on Wednesday. He was arrested by authorities when he fled the scene.

The details of Cruz’s online comments came as former classmates, teachers and neighbors have said they long feared Cruz may have been capable of violence. Cruz, a former student at the school, was expelled last year for disciplinary reasons.

The Marjory Stoneman Douglas shooting is the 6th school shooting resulting in injuries this year. There have been 17 incidents of gunfire in schools this year, according to gun control group Everytown USA. It is also the deadliest school shooting since the 2012 massacre at Sandy Hook Elementary School in Newtown, Connecticut, which claimed the lives of 20 children and six adults.

“This is a terrible day for Parkland, Broward County, the state of Florida and the United States,” Broward Sheriff Scott Israel said at a press conference Wednesday. “It’s just catastrophic. There really are no words.”

Videos and photos posted by students on social media painted a gruesome picture of the shooting, showing blood spilled on the floor of classrooms and bullet holes in the screens of laptops. Text messages shared between students and their family members shared on social media showed teenagers saying goodbye.

Authorities said the gunman used an AR-15 rifle, a semi-automatic weapon made for military use and seen in other mass shootings, including the 2016 Pulse nightclub massacre in Orlando. Florida Sen. Bill Nelson told CNN the suspect also wore a mask and carried smoke grenades during the attack.

“This is just pure evil,” Florida Governor Rick Scott told reporters at a press conference Wednesday evening, where he also pledged “whatever state resources are necessary” to law enforcement or “to help any family member who’s impacted.”

“How could this ever happen in this country? How could this happen in this state?” Scott said, adding that his “prayers are with everybody impacted.”

Here’s what we know about the shooting so far:

17 people were killed

At least 17 people were killed in the shooting on Wednesday, with 12 slain inside the school, according to Sheriff Israel.

Three other victims were shot outside the building and on a nearby street corner, and an additional two victims died at nearby hospitals. Sheriff Israel told CBS and other media that a football coach was among the victims, and added that the son of a deputy sheriff was also shot. According to Israel, five of the 17 victims had still not been identified at 9:30 p.m ET.

Sixteen victims are being treated at local hospitals, according to the Orlando Sentinel, including seven victims at Broward Health Medical Center in Fort Lauderdale. Of those seven, two were in critical condition and five were stable, a doctor told local reporters. Another another nine victims were taken to Broward Health North Medical Center, of whom three were in critical condition.

A doctor at Broward Health North declined to give information about specific patients’ cases, but predicted a positive outcome. “They’re going to have successful surgeries. They’re going to recover. They’re going to go home,” Igor Nichiporenko told reporters.

Another victim was taken to Broward Health Coral Springs, according to the Palm Beach Post.

Broward County Public Schools Superintendent Robert Runcie described the shooting as an “unspeakable tragedy” representing “the worst of humanity,” adding in a statement that the school district was cooperating with law enforcement agencies. “No parent should ever have to send their kids to school and have them not return,” Runcie told reporters. “We’ve got to find a way for this to stop.”

Marjory Stoneman will remain closed for the rest of the week, the Broward County Sheriff’s Department announced. Nearby Westglades Middle School will remain open, and grief counselors will be stationed at a number of nearby locations for students, family members, and school faculty and staff.

The suspect has been identified as Nikolas Cruz

The sheriff’s office identified the suspected shooter as 19-year-old Nikolas Cruz, who was charged Wednesday with 17 counts of premeditated murder. He later confessed to the shooting while in custody, police said.

The suspect had previously attended the school but was expelled for disciplinary reasons, officials said.

Cruz is an orphaned teenager who moved in with a friend’s family after his mother died in November 2017, James Lewis, an attorney for that family, told the AP. While living there, he attended an adult correctional school and worked at a local dollar store.

Students at the school described Cruz as an “outcast” and a “loner” in interviews following the incident. Some said Cruz would talk about his “guns, knives and hunting,” and that “everyone predicted” he would turn into a school shooter.

During the incident, The school was initially placed on lockdown, but started dismissing students as a SWAT team worked on clearing the buildings. Broadcast news footage showed students running from the school building with their hands up.

The FBI said it is working with local law enforcement, and set up a tips page for information or for witnesses to upload photos or videos related to the incident.

The gunman used an AR-15 assault rifle and carried smoke grenades

Israel said that Cruz had one AR-15 semi-automatic assault rifle and “multiple magazines” with him. Gunmen in past mass shootings, including Newtown, the 2017 shooting on the Las Vegas strip and the 2016 Pulse Nightclub shooting in Orlando have used similar style rifles.

Cruz was also wearing a gas mask and equipped with smoke grenades, which he used to set off a fire alarm “so kids would come pouring out of classrooms and into the hall,” Florida Sen. Bill Nelson told CNN. “And there the carnage began.”

Leaders respond: ‘That terrible day you pray never comes’

President Trump spoke with Florida Gov. Rick Scott, who said he will continue receiving updates on the investigation from law enforcement. In a tweet, Trump offered condolences to family members of the victims and said “no child, teacher or anyone else should ever feel unsafe in an American school.”

On the other side of the world at the Winter Olympics in Pyeongchang, South Korea, American figure skating duo Alexa Scimeca-Knierim and Chris Knierim dedicated their pairs skating program to the victims of the shooting. “We wanted to skate for the 17 children that died in the Florida shooting,” Scimeca-Knierim said in an interview after their performance.

Florida Sen. Marco Rubio said he was “devastated” and “saddened” by the deadly shooting, which he called a “clear attack…designed [and] executed to maximize loss of life.” Rubio also said in his statement Wednesday that he hopes authorities can find out in coming hours and days more about how and why the killer carried out the attack. “Today is that terrible day you pray never comes,” Rubio said.

Meanwhile, Connecticut Sen. Chris Murphy — who has become a vocal advocate for gun control legislation in the wake of the Sandy Hook Elementary School shooting in his state — responded to the “horrific scene” while speaking on the Senate floor.

“This happens no where else other than the United States of America, this epidemic of mass slaughter, this scourge of school shooting after school shooting,” he said. “It only happens here — not because of coincidence, not because of bad luck, but as a consequence of our inaction. We are responsible for a level of mass atrocity that happens in this country with zero parallel anywhere else.”

Former Congresswoman Gabrielle Giffords said the shooting should “strike fear into all Americans,” while calling on Congress to enact stricter gun control legislation. “Is it safe to send our kids to school? Are we safe in our homes and communities?” the former Congresswoman, who survived a shooting in 2011 wrote on Twitter.

Florida Congresswoman and former Democratic National Committee chair Debbie Wasserman Schultz said the victims of the shooting “are weighing heavy in my heart” while praising first responders. “This senseless violence must end,” she wrote.

Students and teachers described ‘the worst nightmare’

“This is the worst nightmare that you hope never happens to you,” Melissa Falkowski, a teacher at Marjory Stoneman Douglas who hid 19 students in a classroom closet during the shooting told CNN on Wednesday. “We could not have been more prepared for this situation, which is what makes it so frustrating,” Falkowski said, adding that she felt “like our government, our country has failed us and failed our kids and didn’t keep us safe.”

Senior David Hogg said he heard a fire alarm, the second of the school day, and saw a “flood of people” running toward him, according to the Orlando Sentinel. A TV production student, Hogg pulled out a video camera to record himself and a group of other students who sought safety in culinary instructor Ashley Kurth’s classroom. “It’s horrifying,” Hogg said. “My sister talked to people yesterday that she’ll never talk to again.”

Other students at the high school shared information about what had happened, some while they were still hiding inside the school.

https://twitter.com/morganw_44/status/963929436239298562

Survivors of the shooting demand gun control

The teenagers who survived the shooting at their school have called on the nation’s leaders to immediately work to enact stricter gun control laws to prevent another massacre from occurring in the United States.

In the days after surviving the horrific event, students participated in a protest demanding gun control and more than 100 of them are planning on visiting the state capital in Tallahassee to speak with state lawmakers. On Sunday, students announced their upcoming “March for Our Lives” in Washington, D.C., and at other cities around the country on March 24.

“My message for the people in office is this: You’re either with us or against us,” Cameron Kasky, a junior at the high school, told CNN. “We are losing our lives while the adults are playing around.”

Students like Emma Gonzalez, who gave an impassioned speech Saturday that made waves around the country, have criticized politicians like President Donald Trump, Florida Sen. Marco Rubio and Florida Gov. Rick Scott for accepting donations from the National Rifle Association. Part of the upcoming march, the students have said, is to raise awareness about the lawmakers who have received donations from the NRA and hold them accountable for the mass shootings in the U.S.

This story has been updated to include more context about how Everytown for Gun Safety categorizes an incident as a school shooting.

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Write to Katie Reilly at Katie.Reilly@time.com and Eli Meixler at eli.meixler@time.com.