Investigators in Florida and Saudi Arabia on Sunday dug deeper into the background of a Saudi aviation student who fatally shot three people at a Pensacola naval base, as lawmakers from both parties demanded the kingdom fully cooperate in the investigation.

Officials are treating the shooting as an act of terrorism and are trying to learn whether the gunman was working as part of a larger network when he opened fire in a Naval Air Station Pensacola classroom Friday, killing three people and wounding eight.

Officials sought to reassure Pensacola residents that they knew of no ongoing threat to the area, saying that while investigators pursue a wide variety of interviews and evidence, there was only one gunman behind Friday’s violence.

On the third day of the investigation into the attack at a base where the U.S. military trains pilots from foreign forces, details on what has been learned so far were sparse, tentative and sometimes contradictory.

The gunman, a Royal Saudi Air Force member named Ahmed Mohammed al-Shamrani, was shot dead by a sheriff’s deputy responding to the rampage. Shamrani apparently left hints that he was motivated at least in part by his hatred of American foreign policy and military might.

The weapon used in the attack, a 9mm Glock, was lawfully purchased, Rachel Rojas, the FBI agent in charge of the investigation, said Sunday at a news conference. But she did not describe how it was obtained and brought onto a base where outside weapons are generally not permitted.

Investigators say they believe Shamrani was the author of an anti-American screed posted on Twitter shortly before the shooting, according to a law enforcement official.

The message criticized U.S. policy supporting Israel, saying “decision-makers, the politicians, the lobbyists and the major corporations are the ones gaining from your foreign policy.” The post also said: “Do you expect to transgress against others and yet be spared retribution? How many more body-bags are American families willing to receive?”

Law enforcement officials are being cautious in drawing conclusions too swiftly. Rojas said authorities are treating the shooting as an act of terrorism largely because the designation unlocks investigatory tools. She said they are still trying to “discern any possible ideology that may have been a factor.”

Saudi students close to Shamrani are cooperating and providing information to investigators as their Saudi commanding officer restricts them to the base, Rojas said, adding that the Saudi government has pledged full cooperation. No arrests have been made, she said.

Some of the Saudis are being held for their own protection, said a Saudi official, who like others spoke on the condition of anonymity Sunday to talk openly about the investigation.

Several administration officials were less circumspect about the bloodletting that unfolded in a classroom on base.

National security adviser Robert O’Brien said on CBS’s “Face the Nation” that it “appears” to have been a terrorist attack and that Shamrani may have been radicalized in the United States.

Adding to suspicion that the shooter had accomplices, Defense Secretary Mark T. Esper said on “Fox News Sunday” that “one or two” Saudis acquainted with Shamrani filmed at least part of the attack, though it was unclear at what point the videos began.

The FBI said they have recovered base surveillance videos and cellphone videos, including those that a “bystander” took after the attack started and after first responders arrived.

But investigators say they do not believe there is anything nefarious about the video recordings made by multiple people, including a Saudi national, near the scene, according to law enforcement officials.

The videos were recorded across a street and well after the shooting began, indicating they were the kind of recordings that any passerby witnessing a dramatic incident might take, the officials said.

Tamping down concern that more collaborators might be at large, an FBI spokesman said, “To confirm, we are not aware of any credible threat to the community at this time.”

Even with so many basic elements unresolved, the incident threatens to drive another wedge into the uneasy relationship between the United States and Saudi Arabia.

Many in Congress have expressed outrage over the Saudi-led war against Houthi rebels in Yemen, which the United States has supported with military assistance. And an investigation into who in the Saudi hierarchy was involved in the 2018 killing of Jamal Khashoggi, a U.S. resident and contributing columnist for The Washington Post, remains opaque and incomplete.

That has raised skepticism among some members of Congress that the Saudis are prepared to cooperate, as O’Brien said they have committed to do.

Rep. Matt Gaetz (R-Fla.), one of several officials in the state calling for closer scrutiny of foreigners who enter the country for military training, said on ABC News’s “This Week” that he spoke with Reema bint Bandar, the Saudi ambassador to the United States, who called to offer condolences.

Gaetz said he told the ambassador that the United States does not want Saudi Arabia interfering in the case but expects its full cooperation should investigators need it.

Gaetz raised the possibility that Shamrani had collaborators in the attack, which the congressman deemed terrorism.

“If there are Saudis that we do not have — that may have been involved in any way in the planning, inspiration, financing or execution of this,” he said, “we expect Saudi intelligence to work with our government to find the people accountable and hold them responsible.”

The lawmaker said the ambassador assured him that full cooperation would be provided.

Rep. Adam B. Schiff (D-Calif.) struck a similar tone Sunday on CBS News’s “Face the Nation,” saying officials would press Saudi Arabia to investigate the tragedy.

He also accused President Trump of not being aggressive enough with the kingdom.

“I wish the president was pressing the Saudi government for answers,” Schiff said.

Trump’s response to the shooting has been conspicuously restrained. On Friday, the president tweeted that he had spoken with Saudi King Salman by phone and that the royal was “greatly angered by the barbaric actions of the shooter and that this person in no way, shape or form represents the feelings of the Saudi people who love the American people.”

On Saturday, the president said the king was “very, very devastated by what happened and what took place. Likewise, the Crown Prince. . . . And I think they’re going to help out the families very greatly.”

White House officials stressed that the attack would not affect the close relationship with Riyadh.

In Pensacola, base security practices are under scrutiny amid questions about how the attack was carried out.

Air Force Gen. Terrence O’Shaughnessy, who oversees U.S. base security as chief of U.S. Northern Command, has directed domestic bases and units to “immediately assess force protection measures and implement increased random security measures for their facilities,” Northcom said in a tweet early Sunday.

Shane Walters, the father of one of the victims, Cameron Scott Walters, blamed what he said was a “huge breach” in base safety for the death of his son. The 21-year-old was gunned down as he stood watch at the base classroom building where law enforcement found a grim scene of bodies, blood and broken glass, his father said.

Walters said he would not let his other children join the military he was so proud to serve in.

“Why would I condone my children joining the military when we can’t protect them on our own military bases?” he said.

The FBI has identified the other two victims as 23-year-old Joshua Kaleb Watson and 19-year-old Mohammed Sameh Haitham. All three were Navy students.

Alice Crites, Dan Lamothe, Ellen Nakashima, T.S. Strickland and Marisa Iati contributed to this report.