SAN BERNARDINO, Calif. (AP) — 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 massive 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 described the 27-year-old Friday as "just a housewife" who was quiet like her husband and strictly followed Muslim custom. She wore traditional clothing that covered her face so that her brothers-in-law didn't even know what she looked like, according to the lawyers who represent Farook's mother and three siblings.

Authorities say she ditched the Muslim garb for a combat-style outfit Wednesday, when she and Farook attacked the holiday party in San Bernardino. A few hours after the killings, 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 other foreign terror group.

"The investigation so far has developed indications of radicalization by the killers and of potential inspiration by foreign terrorist organizations," Comey said. He cautioned that the investigation has not yet shown evidence the couple was part of a larger group.

Despite signs of the couple's radicalization, there "is a lot of evidence that doesn't quite make sense" at this early stage, he said.

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

"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.

David Bowdich, head of the FBI's Los Angeles office, said "a number of pieces of evidence" point to terrorism and that the agency was focused on that idea "for good reason." He would not elaborate.

Bowdich said investigators were looking carefully to determine if there is a connection to IS.

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.

Farook and Malik rented a townhome in Redlands, a few miles from the attack scene, where investigators said they found an arsenal of ammunition and homemade bombs.

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.

While it appeared unseemly, Bowdich said the FBI had finished investigating the home. Among things authorities had 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 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.

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 FBI questioned her Wednesday night and, according to the attorneys, said they would not release her until Farook's siblings came for questioning.

The couple's orphaned daughter is in the care of child protective services 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, moved from her home country of Pakistan to Saudi Arabia and eventually came to the U.S. in 2014 on a fiancee 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.

Nadvi said FBI agents have questioned the mosque's leaders about the couple.

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. Using slick propaganda, 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.