Hours after Syed Farook and his wife, Tashfeen Malik, mowed down 14 people at a center for the disabled in San Bernardino on Wednesday, the murderous duo were hurtling down a residential street in a police chase that quickly escalated.

Malik, 27, fired the first shots out the back of their rented black Ford Expedition in a shootout with 23 officers that left both suspects dead.

Farook, an environmental specialist at the county health department, had abruptly left a holiday party for San Bernardino County health employees held at a facility for handicapped people.

He returned with Malik, both dressed in combat gear and spraying bullets from AR-15 assault rifles.

The couple had a child together, a 6-month-old daughter whom they dropped off with Farook’s mother on their way to the holiday party.

On Friday morning, federal investigators told CNN that Malik had pledged allegiance to ISIS on Facebook around the time of the shooting.

She posted her pledge under an account with a different name, officials said. But the ISIS connection is murky: Officials did not clarify how they determined Malik was responsible for the post. And intelligence officials caution that there may be less to the ISIS link than initial reports suggest.

That said, FBI Assistant Director David Bowditch announced on Friday that the massacre was officially being investigated as a terrorist incident.

“There’s a number of pieces of evidence that have essentially pushed us off the cliff,” he said at a press conference. “We are now investigating that this is now an act of terrorism.”

Information about the suspects, including evidence that they may have been inspired by radical Islam, has slowly leaked out in the four days since the massacre.

Fresh reports have homed in on Malik’s apparently significant role in the attacks, even if the couple’s precise motives remain shrouded in mystery.

Neither Malik nor Farook had ever been monitored by Feds as potential radicals, and neither one has a criminal record. But the stockpile of weapons at their house suggests that the couple was considering carrying out a deadly crime on a massive scale.

The New York Times and other media outlets quoted anonymous officials who said they’d found evidence that Farook was communicating with domestic and international extremists.

For the time being, federal law enforcement officials have offered no explanation for the attack beyond suggesting that it was a “combination of terrorism and workplace [violence].”

In the aftermath of the atrocity, the idea of Malik wielding an assault rifle as though she were a trained militant has become the focus of media attention.

Indeed, female shooters in the U.S. are a statistical anomaly. A 2014 FBI report revealed that only six of the 160 “active shooter” incidents between 2000 and 2013 were perpetrated by women.

Other female mass shooters in the last 40 years can be counted on one hand: Amy Bishop, who shot six University of Alabama Huntsville colleagues at a faculty meeting in 2010, killing three of them; Jennifer San Marco, a onetime U.S. Postal Service worker who in 2006 murdered six employees at the processing plant where she used to work; Brenda Spencer, who was 16 when she fatally shot two adults and wounded eight children at a San Diego elementary school in 1979.

Where these mentally ill women had “snapped,” Malik demonstrated more skill and apparent deliberation in her attack with Farook.

If the mass shooting does turn out to be an act of terrorism, experts say it isn’t unusual for women to have prominent roles within extremist groups.

“There is a possibility that Malik pushed Farook from being a devout, moderate Muslim to a more radical one,” said Mia Bloom, professor of communication at Georgia State University, who specializes in the role of women in terror organizations.

“It’s not at all unheard of for women to be the radicalizing force,” Bloom added.

She cited Sajida Mubarak Astrous al-Rishawi, an Iraqi woman who conspired a suicide bombing mission with her husband in 2005 at a hotel in Amman, Jordan. The couple had been sent by Abu Musab al-Zarqawi, the former al Qaeda leader in Iraq.

As al-Rishawi struggled with the cord on her suicide belt, her husband detonated his at the other end of the Radisson SAS hotel ballroom, killing 38 people. Al-Rishawi survived and, after years of being detained, was executed in Jordan in February.

Al-Zarqawi had also sent Muriel Degauge, a Belgian woman who converted to Islam, on a suicide mission with her husband in Baghdad. Hers was successful; her husband, a Belgian-Morroccan, was killed hours later by U.S. forces in Iraq.

Both al-Rishawi and Degauge are said to have radicalized their husbands, according to Bloom.

Bloom also mentioned Reem Saleh al-Riyashi, who in 2004 became the first Palestinian mother to blow herself up, killing four Israelis after crossing over the Gaza border.

Trained by Hamas militants, al-Riyashi posed with her daughter in her last will and testament videos—a reminder that ideology can trump maternal instinct, as it may have for Malik.

While ISIS does not officially allow women to fight in combat, they released a manifesto this year saying there may be exceptions to that rule. Women are more frequently utilized to recruit Westerners and distribute propaganda online.

“The fact that a woman was involved makes it much more likely to be terrorism,” said Brigitte Nacos, a political science professor at Columbia University who studies women’s roles in terrorism. “I simply do not believe a woman would be so involved if it was any other act of workplace violence. It seems that these two people plotted [the attack] out.”

Jonathan Schanzer, vice president of research for the Foundation for Defense of Democracies and the author of the new book State of Failure: Yasser Araft, Mahmoud Abbas and the Unmaking of the Palestinian State, said: “There are precedents for women suicide bombers going back to the days of the PLO, but this is different. Tashfeen Malik was doing the shooting. That is something that there is very little precedent for.”

If Farook and Malik’s rampage was inspired by ISIS, the couple may have been radicalized recently (radicalization for the group can occur within a matter of weeks, much shorter than other terrorist organizations).

A rapid radicalization framework might have caused them to act on any random trigger, like a workplace dispute.

Farook grew up in the United States and was described as a devout, well-intentioned Muslim by members of a local mosque where he worshiped.

In 2013, he told them he was traveling to Saudi Arabia on hajj, a religious pilgrimage, and to meet his fiancée, Malik.

Farook and Malik reportedly met through a dating website where Farook wrote that he came from a “religious but modern family” on his profile and listed interests including “working on vintage and modern cars” and “hang[ing] out in back yard doing target practice with younger sister and friends.”

Malik had lived with her family in Saudi Arabia, where Wahhabi clerics promote the most extreme interpretation of Islam, for 25 years before she moved to the U.S.

Officials have confirmed they were married in 2014 at the Black Stone, the center of the Grand Mosque of Mecca.

In July 2014, Farook traveled to the United States with Malik, who arrived with a Pakistani passport and a 90-day fiancée visa. She applied for a green card in September—a process that requires passing counterterrorism background checks—and was granted one in July 2015.

In an interview with CBS, Farook’s longtime coworker, Christian Nwadike, said he seemed different after returning from Saudi Arabia and attributed his radicalization to Malik. “I think he married a terrorist,” he said.

His fellow worshipers in San Bernardino said Farook prayed at their mosque regularly for years and had recently memorized the Quran—then suddenly disappeared three weeks ago.

“I feel there is a key piece of the puzzle we are missing here,” Schanzer said. “They had just gotten married and had a baby not that long ago. Who celebrates their love with a mass murder? This doesn't feel like a copycat attack. This doesn't feel quite like anything we've seen on American soil.”

For Bloom, “It seems like they were preparing something big. Then something pissed him off at the holiday party and he went home and told [Malik] to put her body armor on.”

Bloom noted that a work party is not a traditional target for terrorism. “It doesn't fit neatly with the rhetoric.”

Schanzer said: “If the reports they met in Saudi Arabia are true, then how did they meet there? You don't go to Saudi Arabia to be single and mingle. There had to be an introduction. Who introduced them?”

Schanzer also said that both Farook and Malik “obviously had a lot of tactical training but where? Maybe they were self-radicalized but that’s weird unto itself. There’s a piece missing.”

Professor Brian Levin, director of the Center for the Study of Hate and Extremism at San Bernardino State, said the roles of women “are being greatly expanded” within radical Islam. “They are being groomed to be a lot more than wallflowers. Women are being recruited too. [Tashfeen Malik] is an incredibly interesting person who might have been one of the catalysts for his [Farook’s] radicalization. The fact that she came from overseas is very significant.

“It could have been someone else or it could have been a mixture. But any way you look at it, this guy [Farook] was an extremist recruiter’s dream. He was clean. He fit the bill. He’s the kind of guy they want to recruit.

“There could be a mixture of motivations. But there is something we call the ‘propaganda of the deed,’ which is when the action and deed speak for themselves and there is no reason for a note or explanation of motive. It can be very effective. I feel they [authorities] know more than they are telling us. I think they know more about them than they are saying.”

Editor's note: An earlier version of this story incorrectly stated that al-Rishawi was still detained in Jordan. She was executed there in February 2015.