Last Updated Jun 20, 2016 4:00 PM EDT
ORLANDO -- As dozens of people finished dancing the night away at a popular gay nightclub in downtown Orlando on June 12, 2016, a gunman opened fire, killing 49 people inside and injuring more than 50 others.
The massacre and standoff unfolded over the course of several hours. The horror began to emerge in the earliest moments, as revealed in a cryptic text message from a son to his mother: "In club they shooting."
Here is a timeline of the Orlando mass shooting:
About 2 a.m., Sunday, June 12
Omar Mateen enters Pulse nightclub armed with an assault rifle, a handgun and multiple rounds of ammunition and opens fire.
An off-duty officer working security for the club opens fire and is soon joined by two other responding officers, but Mateen gets past them and pushes back toward the bathrooms in the rear of the club.
First Orlando Police Department (OPD) radio call transmitted: multiple shots fired at Pulse nightclub.
Additional OPD officers arrive on scene.
"Mommy I love you," a young man inside the club texted to his mother. It was 2:06 a.m.
Mina Justice was sound asleep when she received the first text from her son, Eddie Justice.
"In club they shooting," he wrote.
Mina Justice tried calling her 30-year-old son. No answer.
Alarmed and half awake, she tapped out a response.
At 2:07 a.m., Eddie Justice wrote back: "Trapp in bathroom."
She asked what club, and he responded: "Pulse. Downtown. Call police."
Then at 2:08: "I'm gonna die." Now wide awake, Justice dialed 911. She sent her son a flurry of texts over the next several minutes.
"I'm calling them now.
U still in there
Answer our damn phone
According to OPD, officers from various law enforcement agencies enter Pulse and engage the shooter.
Pulse nightclub posts a status on Facebook:
"Everyone get out of pulse and keep running."
OPD S.W.A.T. (Special Weapons & Tactics) initiated a full call-out.
The gunman contacted a 911 operator from inside Pulse. The call lasted approximately 50 seconds. the FBI released the following transcript:
Orlando Police Dispatcher (OD): Emergency 911, this is being recorded.
Omar Mateen (OM): In the name of God the Merciful, the beneficent [Arabic]
OM: Praise be to God, and prayers as well as peace be upon the prophet of God [Arabic]. I wanna let you know, I'm in Orlando and I did the shootings.
OD: What's your name?
OM: My name is I pledge of allegiance to Abu Bakr al-Baghdadi of the Islamic State.
OD: Ok, What's your name?
OM: I pledge allegiance to Abu Bakr al-Baghdadi may God protect him [Arabic], on behalf of the Islamic State.
OD: Alright, where are you at?
OM: In Orlando.
OD: Where in Orlando?
[End of call.]
Eddie Justice texts his mom again:
"Call them mommy
He wrote that he was in the bathroom at Pulse.
I'm gonna die."
Mina Justice asked her son if anyone was hurt and which bathroom he was in.
"Lots. Yes," he responded at 2:42 a.m.
When he didn't text back, she sent several more messages.
"Text me please," she wrote.
"No," he wrote four minutes later. "Still here in bathroom. He has us. They need to come get us."
Officials say the gunman had the first of three conversations with OPD's Crisis Negotiation Team, a call that lasted approximately nine minutes.
At 2:49 a.m., Mina Justice told her son Eddie that the police were there and to let her know when he saw them.
"Hurry," Eddie Justice wrote. "He's in the bathroom with us."
She asked, "Is the man in the bathroom wit u?"
Eddie Justice texts his mom: "He's a terror."
Mina Justice receives a final text message from her son, Eddie, a simple one word answer: "Yes."
She will not hear from him again.
The gunman engages in a second call with OPD's Crisis Negotiation Team, lasting approximately 16 minutes.
Officials say a third crisis negotiation call occurred, lasting approximately three minutes.
Investigators later revealed details of the three calls. When a police negotiator asked the shooter what he had done, he replied: "No, you already know what I did." The shooter continued, stating, "There is some vehicle outside that has some bombs, just to let you know. You people are gonna get it, and I'm gonna ignite it if they try to do anything stupid."
At one point, the shooter stated that he had a vest, and further described it as the kind they "used in France." The shooter later stated, "In the next few days, you're going to see more of this type of action going on."
The shooter hung up and multiple attempts to get in touch with him were unsuccessful, police said.
Orlando Regional Medical Center personnel receive an urgent message on their pagers: "Mass casualty is in effect due to active shooting more than 20 traumas."
Orlando police say they are responding to a shooting at a nightclub in Florida.
A post on the department's official Twitter account said "multiple injuries" have been reported following the incident at the Pulse Orlando nightclub near Orange Avenue and Kaley Street. The department advises people to stay away from the area.
Multiple emergency vehicles respond, including the Orlando Fire Department's bomb squad and hazardous material team.
Orlando police pulled an air conditioning unit out of a Pulse dressing room window for victims to evacuate.
As victims were being rescued, they told police the shooter said he was going to put four vests with bombs on victims within 15 minutes.
OPD S.W.A.T. officers and the Orange County Sheriff's Office Hazardous Device Team detonate an explosive charge to breach a wall and use an armored vehicle to make entry into the nightclub.
Police post a message on Twitter saying a loud noise near the scene of the nightclub shooting was a "controlled explosion."
OPD radio communication states that shots were fired.
Orlando police officers report that they "engaged the suspect" and the suspect was down.
OPD Chief John Mina later said that as police entered the club, one officer was injured by gunfire, saved only by his Kevlar helmet.
Officers were able to rescue about 30 hostages and lead them to safety.
Police describe the incident as a "mass casualty situation," but do not release specifics on the number of dead or wounded.
Police announce that the gunman, later identified as Omar Mateen, is dead.
Police say multiple people have been killed inside the Florida nightclub, and at least 42 wounded people have been taken to hospitals.
Orlando Police Chief John Mina says authorities have not determined an exact number of people killed, but that "approximately 20" have died.
Florida Department of Law Enforcement Special Agent in Charge Danny Banks says the mass shooting is being investigated as an act of terrorism.
President Obama is briefed by his homeland security and counterterrorism adviser about the shooting.
Press secretary Josh Earnest says in a statement that the president has directed federal officials to provide "any necessary assistance to pursue the investigation and support the community."
Florida's governor says he is headed to Orlando.
Gov. Rick Scott says in a statement that his thoughts and prayers are with the victims and their families.
The statement thanks the first responders, and says he'll meet with law enforcement and local officials in Orlando.
Scott says: "We will devote every resource available to assist with the shooting in Orlando. Our state emergency operations center is also monitoring this tragic incident."
The suspect in the shooting is publicly identified as Omar Mateen, 29, of Port St. Lucie, Florida.
The death toll rises significantly. At a news conference, police say 50 are dead and there are 53 more hospitalized after the mass shooting at the popular gay nightclub.
Officials later clarify that the death toll included 49 victims plus the gunman, who was killed by police.
Vice President Joe Biden releases a statement about the mass shooting, calling it "an act of pure hate and unspeakable terror."
"They were our brothers and our sisters; our friends, neighbors, and loved ones. In the coming days, we will learn more about these fifty souls and the lives they lived and the world they made better," Biden said.
He offered condolences to the victims and their families.
"The violence is not normal, and the targeting of our lesbian, gay, bisexual, and transgender Americans is evil and abhorrent," Biden said.
Families and friends gather outside Orlando Regional Medical Center, many in tears, waiting to learn whether their loved ones are among those killed.
The leaders of The American Muslim Community Centers, a mosque in Longwood, Florida, near Orlando, release a statement condemning the attack.
"The American Muslim Community Centers is saddened and shocked by the senseless killings in downtown Orlando, and we pray for the victims and their family members," said Atif Fareed, the mosque's chairman. "AMCC and its members offer their deepest condolences to those affected by this tragedy, and we stand with our fellow Americans in this difficult time."
"Ramadan is a month of deep reflection and prayer. Senseless violence has no place in our religion or in our society. We strongly condemn this heinous act of violence against humanity," Fareed said.
Mateen's father says he is in shock and that he wasn't aware of anything his son might have been planning.
Seddique Mir Mateen, of Port St. Lucie, Florida told media that his son got angry when he saw two men kissing in Miami a couple of months ago and thinks that may be related to the shooting.
The father says: "We are saying we are apologizing for the whole incident.... We are in shock like the whole country."
He also says his son's actions had nothing to do with religion.
Sources tell CBS News that the gunman, Omar Mateen, was on law enforcement radar during the last five years, but no formal investigation was opened by the FBI.
Mateen, who has worked previously as a security guard, was not under investigation at the time of the shooting.
A law enforcement source tells CBS News senior investigative producer Pat Milton that investigators are seeking search warrants for Mateen's residence, car, and communication devices, including his cellphone and computer.
They are also seeking his financial and phone records to determine who Mateen has been in contact with, and in particular if he was communicating with anyone overseas.
Members of Congress are briefed on the investigation and are told that Mateen pledged allegiance to ISIS, CBS News correspondent Jeff Pegues reports.
A law enforcement official confirms to CBS News senior investigative producer Pat Milton that Mateen identified himself to the 911 operator, giving his full name. In addition to ISIS, Mateen also mentioned the Tsarnaev brothers, the attackers behind the 2013 Boston Marathon bombing, calling them his "homeboys."
President Obama speaks from the White House about the attack. He says the worst mass shooting in U.S. history is a further reminder of how easy it is for someone to get a weapon that allows them to shoot people in a school, in a house of worship, a movie theater or a gay nightclub.
Mr. Obama says the United States has to decide if that is the "country we want to be." The shooting thrusts the topic of gun control back into focus during the presidential campaign.
The security company G4S confirms that the Orlando shooting suspect was employed as a guard. The company releases a statement saying:
"We are shocked and saddened by the tragic event that occurred at the Orlando nightclub. We can confirm that Omar Mateen had been employed with G4S since September 10, 2007. We are cooperating fully with all law enforcement authorities, including the FBI, as they conduct their investigation. Our thoughts and prayers are with all of the friends, families and people affected by this unspeakable tragedy."
A law enforcement official confirms to CBS news senior investigative producer Pat Milton that shooting suspect Mateen made the Hajj, an Islamic pilgrimage to Mecca, Saudi Arabia, in March 2012.
Staff at the Islamic Center, a mosque in Ft. Pierce, Florida, confirmed to CBS News that Mateen has worshiped at the facility regularly for several years.
The mosque condemns the attack in a statement:
"We condemn this monstrous attack and offer our heartfelt condolences to the families and loved ones of all those killed or injured. The Muslim community of Fort Pierce joins our fellow Americans in repudiating anyone or any group that would claim to justify or excuse such an appalling act of violence."
The terror group ISIS claims credit for the attack.
An ISIS-related Twitter account and website stated that the shooting "was carried out by an Islamic State fighter."
ISIS has in the past claimed responsibility for attacks that did not originate within their command structure or territory.
The FBI confirmed at a press conference that federal authorities twice looked into Mateen in the past. In 2013, Mateen allegedly made inflammatory statements referencing terrorism while talking to coworkers, and in 2014 he was questioned because of what FBI Special Agent Ron Hopper called a possible connection to a suicide bomber.
Hopper said agents contacted Mateen three times, but ultimately determined there was no reason to pursue an investigation.
"Those interviews turned out to be inconclusive so there was nothing to keep the investigation going," Hopper said.
The City of Orlando begins to release names of victims of the nightclub shooting whose next of kin have been contacted.
Officials start removing bodies from inside the nightclub.
Sunday night, workers brought four bodies on stretchers out of club Pulse and loaded them into white vans. The action was repeated over and over.
The ex-wife of the Orlando nightclub gunman says he was "mentally unstable and mentally ill."
Sitora Yusifiy, speaking to reporters in Boulder, Colorado, says Omar Mateen was bipolar and also had a history with steroids.
She says that in the four months they were together he cut her off from her family and regularly beat her. She says that her family visited her and saw she wasn't okay and rescued her from the situation.
Yusifiy says they literally pulled her out of his arms. She says she left all her belongings and have had no contact with him for seven or eight years.
She says Mateen was religious, but she saw no signs of radicalism.
Of the nightclub massacre she says, "there was no sign of any of this at all."
Host James Corden opens the Tony Awards broadcast with a somber message about Orlando.
"Our hearts go out to all of those affected by this atrocity. All we can say is you're not on your own right now. Your tragedy is our tragedy," he said in part, adding: "Hate will never win. Together we have to make sure of that. Tonight's show stands as a symbol and a celebration of that principle."
Across the United States, people gather at vigils honoring the victims of the shooting.
Monday, June 13, 1:10 a.m.
Among the names added to the list of deceased is Eddie Justice, who texted his mother from inside the club saying he was going to die.
ISIS' official radio station, al-Bayan, broadcasts a statement praising the attack. "Allah has enabled brother Omar Mateen, one of the soldiers of the Caliphate in America, to carry out a raid where he was able to infiltrate a Crusaders' gathering at a gay night club in Orlando, Florida. Allah enabled him to inflict heavy casualties amongst the filthy Crusaders. He killed and injured over a hundred of them. This is the biggest raid to be carried in America after the raid of Manhattan 16 years ago," it says.
FBI Director James Comey holds a press conference, echoing President Obama's statement that the Orlando attack was an example of home-grown terrorism. He also outlined the agency's previous interactions with the shooter.
"So far, we see no indication that this was a plot directed from outside the United States and we see no indication that he was part of any kind of network," Comey told reporters.
The intelligence community, Comey said, is "highly confident that this killer was radicalized at least in part through the internet."
Officials release the final list of names of all 49 deceased victims.