SAN BERNARDINO, Calif. — The Pakistani woman who joined her U.S.-born husband in killing 14 people in a commando-style assault on his co-workers is now at the center of a huge FBI terrorism investigation, yet she remains shrouded in mystery.

The FBI acknowledges knowing little about Tashfeen Malik. Those who attended mosque with her husband, Syed Farook, said they know nearly nothing of her. Even Farook’s mother, who lived with the couple and their 6-month-old daughter, knows little, according to attorneys for Farook’s family.

The lawyers on Friday described the 27-year-old as “just a housewife” who was quiet like her husband and strictly followed Muslim custom. She wore traditional clothing that covered her face so her male relatives didn’t even know what she looked like, according to the lawyers for Farook’s mother and three siblings.

Authorities say she ditched the Muslim garb for combat-style gear Wednesday, when she and Farook attacked a training session and holiday luncheon in San Bernardino. A few hours later, they were killed in a shootout with police.

The FBI announced Friday it is investigating the mass shooting as an act of terrorism. If proven to be terrorism, it would be the deadliest attack by Islamic extremists on American soil since Sept. 11, 2001. A U.S. law enforcement official said Malik used a Facebook alias to pledge her allegiance to the Islamic State group and its leader just before the shootings.

FBI Director James Comey would not discuss whether anyone affiliated with IS communicated back, but he said there was no indication yet that the plot was directed by any foreign terror group or that the couple was part of a larger cell.

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“The investigation so far has developed indications of radicalization by the killers and of potential inspiration by foreign terrorist organizations,” Comey said. He added that there “is a lot of evidence that doesn’t quite make sense” at this early stage.

In Pakistan, a relative of Malik said the young woman apparently became a more zealous follower of the Muslim faith in the past few years.

Hifza Batool told The Associated Press on Saturday that other relatives have said that Malik, who was her step-niece, used to wear Western clothes but began wearing the hijab head covering or the all-covering burqa donned by the most conservative Muslim women about three years ago.

“I recently heard it from relatives that she has become a religious person and she often tells people to live according to the teachings of Islam,” said Batool, 35, a teacher who lives in Karor Lal Esan, about 280 miles southwest of the Pakistani capital of Islamabad.

The Farook family attorneys, Chesley and Mohammad Abuershaid, said none of his relatives had any indication either Farook or his wife held extremist views.

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“If the most evidence there is to any affiliation is a Facebook account under another person’s name ... then that’s hardly anything at all,” Chesley said.

He and Abuershaid said the family was shocked by the attack and mourns for the victims. They cautioned against rushing to judgment on their motivations.

A Facebook official said Malik praised Islamic State in a post at 11 a.m. Wednesday, around the time the couple stormed a social service center where Farook’s co-workers from San Bernardino County’s health department had gathered.

An Islamic State-affiliated news service called Malik and Farook “supporters” of their Islamist cause but stopped short of claiming responsibility for the attack.

The U.S. official who revealed the Facebook post was not authorized to discuss the case publicly and spoke on condition of anonymity. The Facebook official, who also spoke on condition of anonymity because the person was not allowed under corporate policy to be quoted by name, said the company discovered Wednesday’s post the next day, removed the profile from public view and reported its contents to law enforcement.

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Farook and Malik rented a townhouse in Redlands, a few miles from the attack scene, where investigators found an arsenal of pipe bombs and well over 4,500 rounds of ammunition.

On Friday morning, the property’s owner allowed reporters inside. The surreal scene — reporters walking among baby items, handling family photos and looking at dirty dishes in a sink — was broadcast live on cable TV.

David Bowdich, head of the FBI’s Los Angeles office, said the FBI had already finished investigating the home. Among the things authorities found were two cellphones that had been crushed in an apparent attempt to destroy the information inside. Investigators were trying to retrieve the data.

“We hope that will take us to their motivation,” Bowdich said.

Until Friday, federal and local law enforcement officials said that terrorism was a possibility but that the violence could have stemmed from a workplace grudge. The Farook family attorneys said he told relatives he had been teased at work about his beard.

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They described Malik as a devoted home-keeper who closely followed religious traditions. They said Farook’s mother never saw any of the weapons or bombs authorities found.

The couple’s orphaned baby daughter is in the care of social service authorities, and the family will try to recover her next week.

Farook had no criminal record, and neither he nor his wife was under scrutiny by local or federal law enforcement before the attack, authorities said.

Malik, 27, was from Pakistan but spent time in Saudi Arabia and eventually came to the U.S. in 2014 on a fiancée visa. Farook, a restaurant inspector for the county, was born in Chicago to Pakistani parents and raised in Southern California.

Farook went to the Dar Al Uloom Al Islamiyah of America mosque in San Bernardino every day but abruptly stopped coming three weeks ago. While many members said they knew Farook and described him as quiet and very studious, “no one knows anything about his wife,” said Mahmood Nadvi, son of the mosque’s founder.

Law enforcement officials have long warned that Americans acting in sympathy with Islamic extremists — though not on direct orders — could launch an attack inside the U.S. The Islamic State in particular has urged sympathizers worldwide to commit violence in their countries.

Others have done so. In May, just before he attacked a gathering in Texas of people drawing cartoons of the Prophet Muhammad, a Phoenix man tweeted his hope that Allah would view him as a holy warrior.

Two weeks ago, with Americans on edge over the Islamic State attacks in Paris that left 130 people dead, Comey said that U.S. authorities had no specific or credible intelligence pointing to an attack on American soil.

Since March 2014, 71 people have been charged in the U.S. in connection with supporting IS, including 56 this year, according to a recent report from the George Washington University Program on Extremism. Though most are men, “women are taking an increasingly prominent role in the jihadist world,” the report said.