The deadliest US mass shooting so far in 2018 took place in South Florida on Wednesday.
Authorities arrested a single suspect, a 19-year-old named Nikolas Cruz who had been expelled from the high school where the shooting took place in the town of Parkland, on the edge of the Everglades.
As of Thursday afternoon, 17 people had been confirmed dead, and others were in hospital.
Here, moment by moment, is how the event unfolded.
Wednesday, February 14, 2018: At 2:19 p.m., an Uber car dropped off the gunman at Marjory Stoneman Douglas High School in Parkland, Florida, near Fort Lauderdale. Here's an Instagram photo believed to show the suspect, Nikolas Cruz, posing with a toy gun.
Wednesday, February 14, 2018: At 2:19 p.m., an Uber car dropped off the gunman at Marjory Stoneman Douglas High School in Parkland, Florida, near Fort Lauderdale. Here's an Instagram photo believed to show the suspect, Nikolas Cruz, posing with a toy gun. (Instagram/cruz.nikolaus)
2:21 p.m.: He then entered a stairwell with a black rifle bag. He readied his rifle and began shooting into several rooms.
Footage broadcast by CBS, which shows students hiding while gun shots are heard nearby. (CBS News)
Law enforcement officials have said the gunman pulled the fire alarm before shooting so that people would run into his line of fire.
2:35 p.m.: Some of the first signs to the outside world that a shooting was underway come from social media. One Twitter user noted that students were texting the about the shooting.
2:53 p.m.: Twenty minutes later the Broward County Sheriff's Office publicly acknowledges that a shooting is underway.
The shooter's exact movements inside the school are not clear. This video was recorded by a student inside a classroom, where gunshots and screaming can be heard.
2:55 p.m.: Local media report five injuries in the shooting, the first sense of its scale.
People are told to avoid the area. Cruz reportedly attacked rooms on the first and second floor, before dropping his rifle and backpack on the third floor.
3:01 p.m.: Amid the chaos, police say, Cruz tried to flee with other students. He went to a nearby Walmart and bought a drink at Subway. He left the Walmart and sat down at a McDonald's.
3:01 p.m.: Amid the chaos, police say, Cruz tried to flee with other students. He went to a nearby Walmart and bought a drink at Subway. He left the Walmart and sat down at a McDonald's. (Google Maps)
3:10 p.m.: A student tweets an image of the inside of his classroom where he and classmates are hiding.
3:11 p.m.: Sheriffs confirm that the shooter remains at large.
3:15 p.m.: Students are seen running from the school grounds.
Deputies said that Cruz tried to hide himself among the students running away from the shooting.
They eventually identified him by examining surveillance footage and picking him out from the crowd. A witness told the Miami Herald newspaper that Cruz had put on a military ROTC uniform like those used in class while he was running.
3:41 p.m.: Cruz is arrested without incident around a mile from the school by the neighboring Coconut Creek Police Department. The incident is recorded by a news helicopter.
At about the same time, President Donald Trump sends his "prayers and condolences" to victims.
Shortly after the tweet, some students who survived the shooting responded in anger.
Shortly after the tweet, some students who survived the shooting responded in anger. (Twitter)
4:11 p.m.: Sheriffs confirm that the suspect had been arrested. Cruz is not yet named.
4:27 p.m.: Cruz exhibits "labored breathing" after his arrest and was taken to hospital as a precaution. Local news outlets photographed him being loaded up for the journey.
4:22 p.m.: Sheriffs say 14 people were shot. The figure later increases.
4:30 p.m.: The Associated Press reports that the shooting resulted in "numerous fatalities," the first indication that victims had died.
Family members embracing after the shooting at Marjory Stoneman Douglas High School on Wednesday. (AP Photo/Wilfredo Lee)
4:34 p.m.: The first videos of the arrest emerge.
4:59 p.m.: Sheriffs say students are still inside the school and are being removed from classrooms by SWAT teams. The school has about 3,100 students.
The front side of Marjory Stoneman Douglas High School, located in Parkland, Florida. (Formulanone via Wikimedia Commons)
5:15 p.m.: Video on social media shows SWAT teams evacuating students from their hiding places.
5:30 p.m.: Local and national media begin to name the suspect as Nikolas Cruz. Some initially spell his first name Nicolas, or Nikolaus.
5:39 p.m.: Parents, who were being held at a staging area near the school, begin to be reunited with their children.
6:27 p.m.: Authorities confirm deaths for the first time (previous statements referred only to "victims"). Their death toll is 17.
Business Insider has been keeping track of the identities of those killed and wounded in the attack. Click here for a full rundown.
7:36 p.m.: Media outlets are allowed to get close to the outside of the school. The local channel WSVN broadcasts footage of classroom windows with bullet holes.
8:24 p.m.: A local correspondent tweets a clear photograph of the suspect.
Thursday 15th February, 5:39 a.m.: Reporters watch Cruz getting booked in to the Broward County Jail.
Around 6:30 a.m.: Sheriffs publish jail booking details for Cruz, including his mugshot. He is charged with 17 counts of premeditated murder.
A police mugshot of Nikolas Cruz. (sheriff.org)
The entry is hosted on the Broward County Sheriff's website.
It lists Cruz's date of birth, physical characteristics, and lists the 17 separate murders with which he has been charged.
7:12 a.m.: Trump tweets, saying the shooter was "mentally disturbed."
8:22 a.m.: A teen who survived the shooting pleads for action, saying "we're children. you guys are the adults. You need to take some action and play a role."
Throughout the morning, we learn new details about Cruz's personal history. Cruz was adopted. He had been living with the family of a classmates since both of his adoptive parents are deceased, ABC News reported.
8:33 a.m.: BuzzFeed News' Tom Namako reports that Cruz legally purchased the AR-15 that he used to carry out the shooting.
Read more about Florida's gun laws here »
Around 10:30 a.m.: FBI special agent Robert Lasky confirms that a YouTube user named Nikolas Cruz posted, "I'm going to be a professional school shooter" in the comments section of a video in September.
FBI special agent Robert Lasky. (USA Today)
The FBI was unable to confirm whether the account that made the comment belonged to Cruz, the suspected school shooter.
11 a.m.: Trump addresses the country.
11 a.m.: Trump addresses the country. (Carolyn Kaster/AP)
"It is not enough to simply take actions that make us feel like we are making a difference," Trump said. "We must actually make that difference."
The speech focused on combatting mental health. Trump also said he plans to visit Parkland to console families and local officials at some point in the near future.
After Trump's speech, Florida Gov. Rick Scott said he intends to meet with state leaders next week in Tallahassee to discuss potential legislation dealing with mental health.
After Trump's speech, Florida Gov. Rick Scott said he intends to meet with state leaders next week in Tallahassee to discuss potential legislation dealing with mental health. (Associated Press/Wilfredo Lee)
"The violence has to stop. We cannot lose another child in this country to violence in a school," Scott said at a news conference on Thursday. "If someone is mentally ill, they should not have access to a gun … None of us want anything like this to happen again."
12:12 p.m.: Former President Barack Obama tweets in support of "common-sense gun safety laws."
12:51 p.m.: The AP reports that the leader of a white nationalist group — called the Republic of Florida — claimed Cruz was a member of the organization.
Jordan Jereb told The Associated Press that his group, Republic of Florida, wants Florida to become its own white ethno-state. ROF describes itself as a "white civil rights organization fighting for white identitarian politics," according to the Anti-Defamation League.
He added that he didn't know Cruz personally and that Cruz "acted on his own behalf of what he just did and he's solely responsible for what he just did."
Around 2 p.m.: A judge ordered Cruz held without bond on 17 murder charges.
Nikolas Cruz makes an appearance before Judge Kim Theresa Mollica in Broward County Court, Thursday, Feb. 15, 2018, in Fort Lauderdale, Fla. (South Florida Sun-Sentinel/Susan Stocker via Associated Press)