Orlando terror attack: What we know

FBI investigation: The FBI interviewed the shooter in 2013 and 2014, FBI Assistant Special Agent in Charge Ronald Hopper said. "Those interviews turned out to be inconclusive, so there was nothing to keep the investigation going." He was not under investigation at the time of Sunday's shooting and was not under surveillance, Hopper said.

Mateen was the subject of the 2013 investigation after making comments to co-workers about terrorist ties. The next year, Mateen was interviewed over possible connections to an American suicide bomber. He was not considered a priority subject.

Suspected ISIS sympathizer: Law enforcement officials say Mateen was known to the FBI, one of hundreds of people suspected of being ISIS sympathizers who are on the FBI's radar, according to two law enforcement officials. There was no indication he was plotting to carry out an attack, the officials said. Investigators haven't found evidence to show he was acting on behalf of ISIS. But the knowledge about his possible sympathies explains why they are treating the case as likely Islamic-related terror.

No claim of responsibility: There has been no claim of responsibility for the Orlando nightclub terror attack on jihadi forums, but ISIS sympathizers reacted by praising the attack on pro-Islamic State forums, according to CNN terrorism analyst Paul Cruickshank.

Local mosque reaction: The imam at the Fort Pierce Islamic Center, Syed Shafeeq Rahman, said Mateen was playful and more social when young but had recently kept to himself. He would come to the mosque two or three times a week for two hours and talk to no one. Rahman said he was at Friday prayers -- his usual routine. Rahman said Mateen had been coming to the mosque since 2003. The imam appealed for peace saying: "We have to stop the killing and bloodshed."

High school classmates remember odd statement: Two former high school classmates remember Mateen saying something to the effect Osama bin Laden was his uncle, which caused a lot of brushback from other students. The classmates said that the September 11 attacks seemed to be a significant moment for him and recounted how his mental health may have been affected.

The guns: The shooter purchased a handgun and a long gun within the last few days, Trevor Velinor Bureau of Alcohol, Tobacco, Firearms and Explosives told reporters. "He is not a prohibited person. They can legally walk into a gun dealership and acquire and purchase firearms. He did so. And he did so within the last week or so," Velinor said.

Additional gun found and other details: Investigators recovered an additional gun in the shooter's car. It's a .38-caliber Smith and Wesson revolver, according to a law enforcement official. The ATF is working to trace it. The other two firearms were a Sig Sauer rifle and a Glock pistol, which were traced to the shooter. He bought those two recently (June 4 and 5).

Employment: Mateen worked as a security guard -- allowing him to have a firearms license and minimal background checks when buying firearms. According to a neighbor who saw him regularly, Mateen was a security guard at the St. Lucie County Courthouse. The neighbor said Mateen often worked security in the front of the building, manning the metal detectors.

Caution around claim of responsibility: A message was posted in Arabic on a Dark Web Telegraph site associated with the ISIS news agency Amaq. Some officials have cited the message as a claim of responsibility by ISIS.

Here is CNN's translation: "Sources for Amaq News Agency: the armed attack that targeted a gay nightclub in the city of Orlando in the American state of Florida and that bore more than 100 killed and wounded was carried out by an Islamic state fighter."

But CNN's Salma Abdelaziz, who translated the message and closely monitors ISIS messaging, said:

--The language is inconsistent with previous ISIS announcements.

-- In particular, the Arabic word for gay was used rather than an epithet, the usual approach for ISIS.

-- There was no claim the attack was directed, just an after-the-fact claim the gunman was an ISIS fighter.

The city of Orlando has identified all 49 of the victims killed:

Stanley Almodovar III, 23

Amanda Alvear, 25

Oscar A Aracena-Montero, 26

Rodolfo Ayala-Ayala, 33

Antonio Davon Brown, 29

Darryl Roman Burt II, 29

Angel L. Candelario-Padro, 28

Juan Chevez-Martinez, 25

Luis Daniel Conde, 39

Cory James Connell, 21

Tevin Eugene Crosby, 25

Deonka Deidra Drayton, 32

Simon Adrian Carrillo Fernandez, 31

Leroy Valentin Fernandez, 25

Mercedez Marisol Flores, 26

Peter O. Gonzalez-Cruz, 22

Juan Ramon Guerrero, 22

Paul Terrell Henry, 41

Frank Hernandez, 27

Miguel Angel Honorato, 30

Javier Jorge-Reyes, 40

Jason Benjamin Josaphat, 19

Eddie Jamoldroy Justice, 30

Anthony Luis Laureano Disla, 25

Christopher Andrew Leinonen, 32

Alejandro Barrios Martinez, 21

Brenda Lee Marquez McCool, 49

Gilberto Ramon Silva Menendez, 25

Kimberly Morris, 37

Akyra Monet Murray, 18

Luis Omar Ocasio-Capo, 20

Geraldo A. Ortiz-Jimenez, 25

Eric Ivan Ortiz-Rivera, 36

Joel Rayon Paniagua, 32

Jean Carlos Mendez Perez, 35

Enrique L. Rios Jr., 25

Jean C. Nives Rodriguez, 27

Xavier Emmanuel Serrano Rosado, 35

Christopher Joseph Sanfeliz, 24

Yilmary Rodriguez Solivan, 24

Edward Sotomayor Jr., 34

Shane Evan Tomlinson, 33

Martin Benitez Torres, 33

Jonathan Antonio Camuy Vega, 24

Juan P. Rivera Velazquez, 37

Luis S. Vielma, 22

Franky Jimmy Dejesus Velazquez, 50

Luis Daniel Wilson-Leon, 37

Jerald Arthur Wright, 31

Another 53 people were wounded.

-- Norman Casiano hid in a packed bathroom stall with more than a dozen others, but the gunman shot through the stall door, he said. Some pleaded for mercy, but the gunman responded by firing more bullets. Casiano, struck twice, survived; many in the stall did not.

-- About 300 to 350 people were inside the club.

-- Another survivor hid in the bathroom and covered herself with bodies for protection.

-- Some entertainers hid in the dressing room when the shooting started. They were able to crawl out of the building when police removed the air conditioning unit.

2 a.m. -- Around closing time, about two minutes after 2 a.m., the first shots rang out at Pulse. Witnesses said they thought the noise was part of the music.

Some clubgoers managed to escape. Security and two other officers all fired on the shooter, but the gunman then took hostages.

2:09 a.m. -- Pulse management posted on Facebook: "Everyone get out of Pulse and keep running."

2:22 a.m. -- Mateen called 911 pledging allegiance to ISIS and mentioning the Boston Marathon bombers.

5 a.m. -- A SWAT team used an armored vehicle to smash down a door at the club; 30 more people escaped.

Officers shot and killed Mateen.

The gunman, 29-year-old Omar Mir Seddique Mateen, reportedly expressed outrage when he saw two men kiss -- but also frequented the gay bar he eventually terrorized, sources said.

Pulse performer Chris Callen said Mateen visited dozens of times -- sometimes twice a month.

"He was very friendly when we said hi. He didn't seem like the kind of guy who just did what he did," Callen said. "It makes no sense."

Yet Mateen expressed outrage to his father after seeing two men kissing in Miami, investigators said.

Mateen was born in New York on November 16, 1986. His parents are originally from Afghanistan. Most recently, Mateen lived in Fort Pierce, Florida.

His father, Seddique Mateen, said his son didn't have any mental health issues and showed no signs of being radicalized.

"His act was a terror act, but as far (as) him being a terrorist, I'm not aware," the father said.

The family of the shooter told investigators Mateen wasn't particularly religious from what they saw.

Mateen's ex-wife told investigators he had issues with anger. And former co-worker Dan Gilroy said Mateen often made homophobic, sexist and racist remarks.

"He would hit things and as he was hitting things, he would yell, and of course there was always curse words involved," Gilroy told CNN affiliate WPTV-TV in West Palm Beach. "And this wasn't seldom, this was all the time."

The gunman's father expressed his sympathy to the victims, saying those killed "are my family."

"The people who got injured, they are my family. I care for them. I'm very sad for them."