JUDY WOODRUFF: The search for answers in Orlando is taking authorities down new avenues tonight. Emerging accounts today raised more questions about the man who shot 49 people to death before people shot and killed him.

William Brangham reports from Orlando.

QUESTION: When you saw his picture, what went through your mind?

JIM VAN HORN: We just went, oh, like, yes, that makes sense. There, that's Omar.

WILLIAM BRANGHAM: It's a new wrinkle into the investigation into Orlando shooter Omar Mateen. Some of the patrons of the Pulse nightclub are now saying Mateen was a frequent visitor.

JIM VAN HORN: He used to come in the bar about — on the weekends. Sometimes, he would be there. Sometimes, he would miss a couple of weeks and then be in again. He was a regular.

WILLIAM BRANGHAM: This afternoon, the nightclub's owner said through a spokeswoman that the reports are — quote — "untrue and totally ridiculous."

But the Associated Press reported the FBI is investigating those claims, as well as others that Mateen may have used a dating app for gay men.

KEVIN WEST: The last contact was like three months ago. And as soon as I saw the picture on the news, I quickly noticed the person's face.

WILLIAM BRANGHAM: These allegations come as something of a departure from what was previously said about the attacker. Mateen's father has said his son became upset months ago after seeing two men kissing in Miami, but, otherwise, never seemed homophobic.

Investigators are also talking to the gunman's wife. NBC News reports she told federal agents that she tried to dissuade her husband from carrying out the attack. She also said she was with him when he bought ammunition and a holster, and once drove him to the club because he wanted to scope it out.

Meanwhile, some of those who escaped with their lives spoke today at Orlando Medical Center.

ANGEL COLON, Shooting Victim: I hear him, and he's shooting everyone that's already dead on the floor, making sure they're dead. I look over, and he shoots the girl next to me. And I'm just there laying down. I'm thinking, I'm next. I'm dead.

WILLIAM BRANGHAM: Angel Colon was shot several times. Fighting back tears, he described his rescue by police.

ANGEL COLON: I don't feel pain, but I just feel all this blood on me from myself, from my other people. And he just drops me off across the street, and I look over and there's just bodies everywhere. We're all in pain.

WILLIAM BRANGHAM: All this as the FBI continues to scour the scene of the shooting. Lines of agents and officers worked through the club's grounds this morning, laying down markers and identifying potential clues.

As the investigation here in Orlando ends its third day, there's been a flurry of activity in Washington. President Obama and members of the U.S. House were briefed by top national security officials. Today, the president called again for cracking down on assault-style weapons, and barring those on a terror watch list from buying guns.

PRESIDENT BARACK OBAMA: Otherwise, despite extraordinary efforts across our government, by local law enforcement, by our intelligence agencies, by our military, despite all the sacrifices that folks make, these kinds of events are going to keep on happening.

WILLIAM BRANGHAM: After the session with the president, FBI Director James Comey also briefed members of the House on the investigation, behind closed doors.

And around the country, thousands of Americans are responding in their own ways, with tributes and vigils in a number of cities last night. In New York, supporters gathered in front of the historic Stonewall Inn, where the modern gay rights movement began. And back in Orlando, thousands met in the city's downtown. There, they lit candles and read aloud the names of the 49 killed.

Dew Sizemore, who lost six of his friends to the shooting, said the ceremonies gave him a small sliver of comfort.

DEW SIZEMORE: And I feel like I can leave here and start to heal. And it's the beginning, the beginning of a long road ahead of us, but hopefully tonight will help a lot of people. It helped me.

WILLIAM BRANGHAM: The president is planning on coming here to Orlando Thursday, where he will likely meet with family members and victims of the shooting.

For the "PBS NewsHour," I'm William Brangham in Orlando, Florida.