Patience Carter was trapped in a bathroom with her two friends and the gunman during the Pulse massacre. During a press conference at Florida Hospital on Tuesday, she gave her chilling account of what happened. (Reuters)

ORLANDO — The gunman who opened fire inside a nightclub here said he carried out the attack because he wanted “Americans to stop bombing his country,” according to a witness who survived the rampage.

This account from Patience Carter, a 20-year-old who was inside the club during a three-hour hostage standoff, offers the first glimpse at what the shooter said spurred him to carry out the deadliest mass shooting in American history. Carter said the gunman made his claims about his motivation during the same 911 call in which he pledged allegiance to the Islamic State.

At one point, while about two dozen hostages were in the bathrooms inside Pulse, Carter said the gunman asked if there were any black people in the room. When one man said yes, the shooter said, “‘You know I don’t have a problem with black people,'” Carter recalled during a news conference. She said he added: “‘This is about my country. You guys suffered enough.'”

These comments further add to the uncertainty regarding what may have inspired the gunman, 29-year-old Omar Mateen, who was born in the United States to parents from Afghanistan. At various points, Mateen invoked opposing militant groups, making “inflammatory and contradictory” comments, said FBI Director James B. Comey.

Mateen made at least one other phone call during the standoff, according to two U.S. law enforcement officials, calling an acquaintance he knew from Florida.

Even as investigators continued Tuesday to delve deeper into Mateen’s life, officials have not publicly said what they believe may have motivated him to open fire inside Pulse.

The bloody siege left 49 people dead and more than 50 others injured. Mateen died in a shootout with police after the hostage situation. President Obama said Tuesday that the gunman “was an angry, disturbed, unstable young man who became radicalized.”

Vice President Biden, speaking at an event in New York, suggested Tuesday that the investigation had shown that the incident was “more straightforward” than it initially appeared.

“We are getting to the bottom of this, and it’s becoming clearer and more straightforward than a lot of us even thought,” said Biden, who had attended a national security meeting before the event.

The FBI has said it was exploring whether anti-gay bigotry prompted the attack on the popular gay nightclub. Adding another dimension to the probe, at least two witnesses at Pulse said Mateen had previously visited the club, and they also said they had seen him on Jack’d, a dating app for men.

During his comments in the bathroom, Mateen also claimed to have “snipers outside” the club. The Orlando Police Department said that despite rumors of multiple shooters, which often emerge after mass killings, Mateen was the only gunman at the club.

“It sounded as if he was communicating with other people who were involved with it…. Maybe he was just deranged, maybe he’s just talking to himself, but I honestly feel like I don’t think he was able to pull that off all by himself,” Carter said.

Investigators from the FBI peered deeper Tuesday into the life of the gunman, even as the bureau faced questions and an internal reckoning over whether it missed warning signs during a 10-month probe of the shooter that ended two years before the massacre. During that investigation, the gunman had been placed on a terrorism watch list.

Mateen’s wife, Noor Z. Salman, has increasingly drawn the focus of investigators, officials said. She was involved in helping scout out the club at some point before the attack, according to a U.S. law enforcement official who asked not to be identified. (NBC News first reported that investigators were looking at Salman for this action.)

Seddique Mateen, the gunman’s father, on Tuesday did not respond to questions about whether she hired a lawyer or if he believed she played a role in the attack.

“We’ll wait for the law enforcement,” he said in remarks outside his home in Port St. Lucie, Fla.

A U.S. law enforcement official said Tuesday there were no imminent criminal charges against her.

In Orlando, the toll of the shooting was still unclear. A surgeon at the hospital treating most victims said the number of fatalities could rise.

Hospital officials said Tuesday that six of the people injured in the shooting rampage were still critically ill, while five others were in “guarded” condition. All told, 27 of the 44 patients brought to Orlando Regional Medical Center after the shooting remained hospitalized, said Michael L. Cheatham, the chief surgical quality officer at the facility.

During a news conference Tuesday, doctors at Orlando Regional recounted what they saw early Sunday, saying that patients arrived “by the truckload.”

They described seeing people riddled with bullets and injuries, victims with gunshot wounds in their chests, abdomens and pelvic areas. “This was somewhat of a surreal experience,” one doctor said. “We were just given patient after patient after patient.”

The Orange County Medical Examiner’s Office said it expected to complete autopsies on all 49 victims by Tuesday evening. However, because of the ongoing criminal investigation, officials said they would immediately release the autopsy reports.

As hospital workers continue to treat the survivors, the sprawling investigation into the rampage will also look back at two other times Mateen was on the FBI’s radar. He was investigated in 2013 and 2014 — the probe that put him on a watch list — and came up again in 2014 during another investigation, officials say.

Comey said the bureau would “look at our own work, to see if there is something we should have done differently” during its earlier contacts with Mateen. “So far, I think the honest answer is: I don’t think so,” Comey added. “We will continue to look forward in this investigation and backward.”

It was the third time in recent years that someone scrutinized by the FBI later carried out an attack, following the Boston Marathon bombing in 2013 and a planned attack last year on a contest to draw the prophet Muhammad.

In his comments during the 911 call from the club, Mateen referenced the Boston Marathon bombers, according to officials. His claim that he carried out the shooting to prevent bombings echoed a message the younger Boston attacker had scrawled in a note before he was taken into custody by police. The Boston bomber, who was sentenced to death last year, wrote in the note that the U.S. government was “killing our innocent civilians” and that as a Muslim, “I can’t stand to see such evil go unpunished.”

President Obama said Tuesday that the American people stood with those injured in Orlando as well as the people who lost loved ones or were targeted in the attack. Obama, speaking after a meeting with his National Security Council, also said that the investigation has not turned up any suggestions that the gunman was directed by a foreign terrorist organization.

“It is increasingly clear, however, that the killer took in extremist information and propaganda over the Internet,” said Obama, who plans to travel to Orlando on Thursday. Obama said that the Islamic State, a militant group also known as ISIS or ISIL, has made its propaganda “pervasive and easily accessible,” and said it appeared the shooter in Orlando “absorbed some of that.”

The investigation into the Orlando shooting is delving into a thorny series of factors. While the gunman pledged allegiance to the Islamic State during during his standoff with police Sunday, during this call and at other points over the years he referenced rival extremist groups, leaving his precise sympathies unknown, Comey said. Earlier this week, Obama said the shooting appeared so far to be a case of “homegrown extremism.”

The shooting also occurred during the club’s “Latin Night,” carving deep, painful wounds into the heart of Orlando’s Latino community.

Comey said Monday that investigators were “highly confident that this killer was radicalized, and at least in some part through the Internet,” though he said they were still trying to determine his motives and possible sources of inspiration.

The shooting appeared to exist at a grim intersection, connecting fears of people who may be inspired by extremist groups with concerns about the lone attackers — usually young men — who carry out shooting rampages. Late Monday, an allegedly Islamic State-inspired attacker fatally stabbed a police captain and a government official at the couple’s home outside Paris.

Even though Mateen was born in the United States, the shooting has fueled a resurgent debate on U.S. immigration policy. Republican presidential candidate Donald Trump called Monday for barring immigrants from areas of the world with a history of terrorism as part of a proposed temporary ban on Muslims entering the United States.

During his remarks Tuesday afternoon, President Obama dismissed the suggestion from Trump and others that he use the phrase “radical Islam” when discussing attacks.

“What exactly would using this label accomplish?” Obama asked. “What exactly would it change? Would it make ISIL less committed to trying to kill Americans? Would it bring in more allies? Is there a military strategy that is served by this? The answer is, none of the above. Calling a threat by a different name does not make it go away. This is a political distraction.”

In his remarks, Obama was sharply critical of Trump’s comments about Muslims. During a speech a day earlier, Trump had accused American Muslims of harboring terrorists and accused them — without evidence — of knowing about the attackers in San Bernardino, Calif., and Orlando, and not speaking up to stop them.

Trump has argued against calls for more gun-control laws in the wake of the shooting. Obama, as he has before, again said Tuesday that the country could do more to reduce gun violence.

During a news conference at Orlando Health, survivor Angel Colon described laying on the floor of Pulse as the gunman shot victims on the ground to ensure they were dead. (Reuters)

The political fallout from Orlando also reverberated on the world stage even as it overshadowed the U.S. presidential race. U.N. High Commissioner for Human Rights Zeid Ra’ad al-Hussein called on American authorities to adopt “robust gun control measures.”

“It is hard to find a rational justification that explains the ease with which people can buy firearms, including assault rifles, in spite of prior criminal backgrounds, drug use, histories of domestic violence and mental illness, or direct contact with extremists — both domestic and foreign,” the top U.N. human rights official said in a statement.

Amid the public outpouring of grief and anger, the Florida Attorney General’s Office opened an investigation into a proliferation of more than 100 requests on the money-raising GoFundMe site claiming to be seeking donations for victims and their families.

It is possible all are legitimate, but “we just need to go through each one of them,” said Attorney General Pam Bondi.

Goldman and Berman reported from Washington. Brian Murphy, David Nakamura and Missy Ryan in Washington, Zachary Fagenson in Port St. Lucie and James McAuley in Paris contributed to this report.

Further reading:

Orlando’s Latino community hit hard by massacre at nightclub

‘You are not alone’: Lady Gaga breaks down during fierce tribute to Orlando victims

Fact-checking the Clinton and Trump speeches after Orlando

ISIS-inspired attacker kills French police officer and streams it on Facebook

[This story will be updated throughout the day.]