A board member at the Islamic Center of Fort Pierce in Florida talks about Orlando shooter Omar Mateen’s attendance and demeanor. (Lee Powell/The Washington Post)

A board member at the Islamic Center of Fort Pierce in Florida talks about Orlando shooter Omar Mateen’s attendance and demeanor. (Lee Powell/The Washington Post)

Kevin West said he was in the parking lot at the Pulse nightclub at 1 a.m. Sunday when he recognized Omar Mateen walking in.

The men had met more than a year ago when Mateen reached out to West on Jack’d, a dating app for men. They then lost touch until three months ago, when Mateen made contact again, mentioned that he would be in Orlando soon and suggested meeting for a drink. West had also seen Mateen at Pulse multiple times before.

“I remember details,” said West, a 37-year-old Navy veteran. “I never forget a face.”

Later that night, Mateen would kill 49 people inside the gay nightclub in Orlando in the worst mass shooting in U.S. history.

Mateen’s apparent presence on gay dating apps and his previous visits to Pulse, according to West and another witness, added another dimension to the portrait emerging Monday of the man behind the violent rampage.

The gunman who killed at least 49 people in a shooting rampage at an Orlando nightclub has been identified as 29-year-old Omar Mateen. Here is what we know about him so far. (Deirdra O'Regan/The Washington Post)

Cord Cedeno said he had also seen Mateen inside Pulse before, standing at the bar with a drink. “He was open with his picture on the sites; he was easy to recognize,” said Cedeno, 23, of Orlando, who said he was also contacted by Mateen at least a year ago on a dating app.

Mateen and his family had the typical profile of striving immigrants in this country. But there were also hints of darkness in Mateen’s life, according to interviews with relatives, friends, ex-classmates, former co-workers and acquaintances: Being Afghan American meant he stood out in a small South Florida town and was bullied in school. He switched jobs constantly and became increasingly frustrated, unpredictable, sporadically religious and prone to anger.

Some of Mateen’s high school classmates pinpointed a particularly strange moment on Sept. 11, 2001, when they were watching the attack on the World Trade Center unfold on live TV.

[These are the victims of the Orlando shooting]

Four classmates said Mateen cheered and made mocking comments, which got him pulled from class and may have led to his departure from the school. His unusual behavior that day was also corroborated by other classmates in public posts on Facebook.

The Martin County School District referred all questions about Mateen’s time as a student to the FBI.

Robert Zirkle, then a freshman in the Martin school district, said that after 9/11, he saw Mateen excited and making fun of how America was attacked. “He was making plane noises on the bus, acting like he was running into a building,” Zirkle recalled. “I don’t really know if he was doing it because he was being taught some stuff at home or just doing it for attention because he didn’t have a lot of friends.

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“We all rode the same bus. We weren’t really close friends, but friends at least a little,” he said. “After 9/11 happened, he started changing and acting different.”

At the time, Mateen was attending the Spectrum alternative school, a campus in Stuart, Fla., for students with behavioral issues. One former student who was sitting in the same class as Mateen said he remembers the morning of 9/11 clearly: “Teachers said, ‘Turn on the TV.’ We see the one plane hit. And then see the second plane hit. . . . He was smiling. It was almost like surreal how happy he was about what had happened to us.”

The former student said Mateen stood up after the second tower was hit and claimed that Osama bin Laden was his uncle. “Back then, we didn’t even really know who Osama bin Laden was,” the classmate said. “But he talked about shooting AK-47s. . . . He said he shot them and his uncle taught him how to shoot them.”

The ex-classmate spoke on the condition of anonymity for fear that business clients would find out that he attended a school for poorly behaving students. He recalled others in the class growing angry. “The teacher could tell we wanted to hurt him. So the teacher grabbed him,” he said, and sent him to the dean’s office.

In a Facebook post, another student similarly described Mateen’s standing up and cheering on 9/11.

A third classmate said he distinctly remembers Mateen’s actions that day because both of them were sent to the dean’s office at the same time for acting out when the towers were hit. That third student spoke on the condition of anonymity because he feared being bombarded by media requests.

“I was sleeping in class and woke up to see people jumping off buildings, so I started swearing and they sent me up,” the former student said. When he arrived at the dean’s office, Mateen was also there, apparently for saying rude things about Americans deserving to be attacked, said this student, who was not in the classroom to witness the comments.

The first former classmate — who was in the classroom — vividly recalled Mateen’s father picking him up after he got in trouble. “I remember his dad walking up,” he said. “And in the courtyard in front of everyone, the dad slapped him right across the face.”

After that day, Zirkle said, “he kept doing it and saying crazy things. It’s weird. He was totally cool before 9/11, and then something changed.”

Zirkle and others think Mateen was suspended or expelled from the school shortly afterward.

But such memories don’t fit with those of Kenneth Winstanley, a friend of Mateen’s in junior high and high school, who said he did not recall Mateen celebrating the Sept. 11 attacks and doubted his friend would have done that. Winstanley was not in the same room as Mateen that day.

“I never heard about him doing anything like that,’’ said Winstanley, who attended school with Mateen from grades six through 10. “Someone would have said something. We were friends. If he was caught celebrating something like that, he would have gotten beaten up.’’

Winstanley said he never saw signs of radicalization in Mateen in high school, adding, “I know Omar liked America.’’ He said the two once had a conversation about Mateen’s Muslim faith. “Omar explained the Muslim religion to me,’’ Winstanley said. “He didn’t go crazy into it. It was just some of the things his culture does, the food they eat. Nothing radical Islam at all.’’

Sarah Zaidi, who was best friends with one of Mateen’s three sisters, described the Mateens as “an all-American family.”

“His mom worked for a while at a day-care center. His dad did stuff with stocks and investment,” Zaidi said. “They were pretty moderate as Muslims. None of the sisters or mom even wore a headscarf like some Muslims do.”

Two of Mateen’s sisters are now married and have kids in the same area, Zaidi said. A third is a hairdresser and cosmetologist.

But as the only son, Mateen seemed to have fewer friends than his sisters.

“He was brutally bullied,” said Justin Delancy, who rode the bus with Mateen for several years. “He was a chubby kid and got bullied about his weight. He was probably one of the only kids of [Afghan] descent. That made him stand out a bit as well.”

On some mornings, kids wouldn’t let Mateen sit beside them. On others, he’d get slapped on the back of his head, Delancy said. “He’d try to joke and laugh and make fun of himself to get the attention off of himself. But it didn’t work.”

Court records released Monday depict a meandering life for Mateen after he left the alternative school. He graduated in 2006 from Martin County’s adult vocational school, where struggling students go to get GEDs. He earned an associate’s degree from Indian River State College in 2006.

In the court documents, Mateen disclosed his work history, a string of jobs from 2002 to 2006 at GNC, Hollister, Gold’s Gym, Nutrition World, Walgreens, Chick-fil-A, Circuit City and Publix.

In 2009, Mateen married Sitora Yusufiy, who has said in interviews that Mateen beat her severely. They separated about nine months later. A judge ruled in 2011 that their marriage was “irretrievably broken.”

After he married a second time, his current wife, Noor Z. Salman, also left him to return to her childhood home in Rodeo, Calif., with their 3-year-old son, acquaintances said.

Friends and co-workers gave conflicting reports about Mateen’s religiosity and personality. To some, he was extremely pious and serious. But others described him chasing girls, going to parties and drinking.

“He was fun,” said Ryan Jones, 27, who said he often went out with Mateen.

Former classmate Samuel King and his friends also hung out with Mateen at the mall, where Mateen worked at the GNC store after high school and King at Ruby Tuesday. Half the workers at the restaurant were openly gay, King said, including himself. “He had to know it, but I never got any sense of homophobia or aggression from him.”

Over the past two days, King and others have revisited their interactions with Mateen, trying to find signs of how he turned into someone capable of such violence.

On Tuesday, Mateen’s father, Seddique Mateen, strongly discounted the possibility that his son was gay.

“I don’t believe he was a whatever you call it,” the elder Mateen told reporters gathered outside his home in Port St. Lucie, Fla.

On Monday, he insisted that his son was not motivated by Islamist radical ideology, describing the 29-year-old as “a good son” who did not appear agitated or angry in the days before the shooting.

In an interview at his home, the father offered no hints about what could have driven his son.

When asked about Mateen’s 911 call pledging loyalty to the Islamic State, his father said he did not believe it was genuine. “I think he just wanted to boast of himself,” he said. “No radicalism, no. He doesn’t have a beard even. . . . I don’t think religion or Islam had anything to do with this.”

His father also glossed over the anger and homophobia that, a day earlier, he recounted witnessing in Mateen after his son saw a gay couple being affectionate in Miami. “He was surprised about it. That was it.”

Though he declined to give any information about the location of his son’s wife, Noor Mateen, he mentioned he had seen his grandson earlier today. He did not respond to inquiries as to whether she hired a lawyer or if he believed she had advance knowledge of the Orlando massacre.

“We’ll wait for the law enforcement,” he said.

In a video posted to Facebook early Monday, the father said: “God himself will punish those involved in homosexuality. This is not for the servants” of God.

Meanwhile, in Afghanistan, government officials were also trying to piece together the family’s background for clues. They said they do not know when Mateen’s father left the country but noted that millions fled after the Soviet Union’s invasion in 1979.

Mateen’s father, however, maintained a strong affiliation with Afghanistan, hosting a television show broadcast from California that weighed in on the country’s political affairs. He also filmed dozens of sparsely viewed, rambling YouTube videos portraying himself as an important Afghan analyst and leader.

The most recent video on the father’s YouTube channel shows him declaring his candidacy for the Afghan presidency. But the timing is strange, coming a year after presidential elections were held in Afghanistan. And the elder Mateen appears incoherent at times in the video, jumping abruptly from topic to topic.

Sitting on his living-room couch, the father said he saw no warning signs up to the day before the shootings — when he last saw his son. “He was well behaved. His appearance was perfect,” he said. “I didn’t see any sign of worrying or being upset or nervous.”

Hull reported from Orlando. Arelis R. Hernández in Orlando; Lee Powell and Zachary Fagenson in Fort Pierce; Tim Craig in Afghanistan; and Julie Tate, Alice Crites, Amy Brittain, Jerry Markon, Brian Murphy and Max Bearak in Washington contributed to this report.