One day after a depraved attack on an Orlando, Fla., nightclub left 49 victims dead and 53 more wounded, investigators are working to learn more about the man they say was the lone shooter: Omar Mateen, who was killed at the scene. The case is being treated as a terrorist investigation.

After being briefed on the case Monday, President Obama said, "It appears that the shooter was inspired by various extremist information" online; he added that "all those materials" are now being scrutinized and "exploited."

The president discussed the Orlando case in the Oval Office, in which he spoke for nearly 15 minutes Monday after being briefed by FBI Director James Comey — who said that Mateen had been on a watch list during a federal investigation, but he'd been taken off of it after the inquiry close down in 2014.

Obama added that investigators haven't seen signs that Mateen was directed by ISIS, noting that the gunman pledged allegiance to the group at a late juncture. Comparing the attack to one that hit San Bernardino, Calif., last December, Obama called it "homegrown extremism."

Families and friends of people who were in the Pulse nightclub have spent the past 24 hours trying to learn whether their loved ones survived, gathering in the street near the scene of the shooting. As of Monday morning, investigators said that 48 of the 49 victims had been identified, and that 24 families had been notified so far.

All victims have now been removed from the scene, and the process of reconstructing the events with forensics techniques is now beginning, Paul Wysopal, special agent-in-charge of the FBI's Tampa division, said at a morning news conference in Orlando.

Police say Mateen, who had come under FBI scrutiny at least twice over potential links to terrorism, carried out the deadliest mass shooting in modern U.S. history with guns he had legally purchased in recent days. Mateen also pledged his allegiance to ISIS in a 911 call during the attack, but officials said they haven't seen a direct link between the gunman and the terrorist group.

The attack targeted Pulse Orlando, a gay nightclub that had been throwing a Latin Night dance party. In a report for NPR, Eileen Holliday depicted the club as "a longtime staple in the gay community" that drew a wide-ranging audience.

We'll update this post as news emerges; here's a look at where things stand:

Timeline Of The Attack

The violence began in the early hours of Sunday, June 12. Drawing from the police summary given Monday morning:

Just after 2 a.m. ET, an Orlando police officer who was in uniform and working at Pulse responded to shots fired. The officer exchanged fire with the attacker near the entrance. More officers arrived; a second gun battle ensued and the gunman retreated into a bathroom, according to Orlando Police Chief John Mina.

"Everyone get out of pulse and keep running," read a message posted to the club's Facebook account at 2:09 a.m. But not everyone got out, and the attack became a hostage situation.

Circumstances then became relatively stable, Mina said, adding that negotiators spoke to the gunman and that no gunfire was heard. Mateen was "cool and calm when he was making those phone calls to us," Mina said. But the police chief added that the police were concerned the attacker might have had an explosive vest or another bomb.

At 5 a.m., police opted to force entry into the club by using an explosive to breach the exterior cinder-block wall of a bathroom full of people near a bathroom where Mateen had holed up. The decision was made out of concern that a "further loss of life was imminent," Mina said.

At the time, Mateen was in a bathroom with 4-5 hostages, Mina said. It was during that time, the FBI's Comey says, that the gunman had three contacts with a 911 dispatcher. Mina says that another 12-15 people are believed to have been in an adjacent bathroom. But when the authorities acted, the explosive breach didn't penetrate the wall completely, and an armored vehicle was used to put a hole in the wall. That's when hostages began to emerge.

"The suspect came out of that hole himself," Mina said, and began firing at police. He was then killed.

Orlando police say 11 officers were involved in that part of the operation, which they say rescued some 30 hostages.

The Investigation, and the Weapons

Police identified the gunman as Omar Mir Seddique Mateen, 29, of Fort Pierce, Fla. A U.S. citizen, Mateen used an AR-15-style rifle and a handgun to carry out the attack, officials said.

An agent with the field office of the Bureau of Alcohol, Tobacco, Firearms and Explosives said Mateen legally purchased the firearms, acquiring them in the past week.

After sitting in on a briefing with FBI Director Comey, NPR's Carrie Johnson reports, "Mateen was on a watch list when the first investigation of him by the FBI began in May 2013, and taken off of the list when the investigation was closed March 2014."

She adds that adds that the FBI would have gotten a notification if Mateen had tried to buy deadly weapons while on the watch list.

The FBI's Wysopal said Monday that some 100 leads have been generated.

The ongoing criminal investigation is in the early stages, said U.S. Attorney Lee Bentley. He added that other potential charges are possible, but officials don't currently believe there's an ongoing threat.

Regina Lombardo of the ATF said her agency traced the weapons and confirmed that their last purchaser was Mateen. She added that a third weapon, which was found in Mateen's vehicle, was still being traced.

The Suspect

Mateen was born in New York and worked as a security guard. He was married and had a 3-year-old son, according to his father, who spoke to the media Sunday.

According to Tampa FBI Assistant Special Agent-in-Charge Ronald Hopper, the FBI had investigated Mateen twice: In 2013, after he "made inflammatory comments to coworkers alleging possible terrorist ties" and in 2014 when the agency evaluated his possible ties to U.S. suicide bomber Moner Mohammad Abu Salha.

As the Two-Way reported yesterday, FBI agents "determined the contact was 'minimal' and did not constitute a threat."

Federal officials who've been briefed on the attack have told NPR's Carrie Johnson that Mateen pledged his allegiance to ISIS in a 911 call before the attack.

Mateen's father has spoken publicly about the attack.

"We are saying we are apologizing for the whole incident," Seddique Mir Mateen told NBC News Sunday. "We weren't aware of any action he is taking. We are in shock like the whole country."

"This had nothing to do with religion," The elder Mateen added. But he also described recent incidents in which his son had been angered by seeing men kissing each other in Miami.

Mateen's ex-wife, Sitora Yusifiy, addressed the media in Boulder, Colo., saying her former husband was mentally unstable and "would get mad out of nowhere." She said she left him with the help of her family, after he became physically abusive and controlling. Yusifiy also said Mateen had a history with steroids.

The Victims

The city of Orlando is updating its public list of those killed in the attack, pending notification of next of kin. As of Monday morning, more than half of the 49 clubgoers who lost their lives had been named; of those who have, their ages run from 20-50 years old.

Orlando is operating a hotline for anyone seeking information about friends or loved ones — the number is 407-246-4357.

NPR is working to provide information about those who lost their lives, on a page devoted to the victims.

Reactions

Orlando residents and others lined up to donate blood Sunday. Dozens of vigils were planned for Sunday in Florida and beyond. LGBT pride events in Washington, D.C., included a remembrance. And in New York, people gathered at the legendary Stonewall Inn last night.

Mateen's employer, the security company G4S, issued a statement:

"G4S is deeply shocked by the tragic events in Orlando this weekend and the thoughts of everyone at G4S are with the victims and their families."Omar Mateen was employed by G4S at a residential community in South Florida and was off-duty at the time of the incident. Mateen was subject to detailed company screening when he was recruited in 2007 and re-screened in 2013 with no adverse findings. He was also subject to checks by a U.S. law enforcement agency with no findings reported to G4S."G4S is providing its full support to all law enforcement authorities in the USA as they conduct their investigations."

The shocking loss of life in Orlando was also mentioned several times during last night's Tony Awards ceremony, including one instance in which Lin-Manuel Miranda, the man behind the record-setting musical Hamilton, recited a sonnet in response to the attack.

Internationally, people in Belgium and Paris — two places that recently saw brutal attacks on civilians — paid their respects and showed their solidarity with Orlando. The Eiffel Tower will be lighted in rainbow colors tonight.

Online, the WeAreOrlando site was set up to provide information about other events, as well as to promote a GoFundMe donation page that was set up by Equality Florida to help the victims and their families.

Both Florida Gov. Rick Scott and Orlando Mayor Buddy Dyer have declared states of emergency over the attack.

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