(CNN) -- Authorities are officially investigating Wednesday's San Bernardino, California, massacre as "an act of terrorism," FBI official David Bowdich said Friday.
Bowdich said a number of pieces of evidence pushed authorities to launch a terrorism investigation. He noted some phone conversations between at least one of the San Bernardino shooters and others are being investigated by federal officials.
No one has been arrested in connection with the massacre. The man and woman who police say were the attackers were killed by police on Wednesday.
The semi-automatic long guns they used were altered, including at least one that was essentially turned into a fully automatic weapon, a law enforcement official told CNN.
Investigators think that as the San Bernardino, California, massacre was happening, female shooter Tashfeen Malik posted a pledge of allegiance to ISIS leader Abu Bakr al-Baghdadi on Facebook, three U.S. officials familiar with the investigation told CNN.
Malik's post was made on an account with a different name, one U.S. official said. The officials did not explain how they knew Malik made the post.
A law enforcement official said it appeared that Wednesday's mass shooting -- which left 14 people dead and 21 wounded before the two attackers, Malik and her husband, Syed Rizwan Farook, were killed in a shootout with police -- may have been inspired by ISIS.
But none of the officials said that ISIS directed or ordered the attack. ISIS has called for people worldwide to launch attacks in its name, but isn't known to have claimed credit for what happened in San Bernardino.
"This is looking more and more like self-radicalization," a law enforcement official said.
Another official said authorities haven't ruled out that others may have influenced this radical view. In addition, the law enforcement source said investigators have a greater focus on whether the shooting occurred after a workplace issue with religion.
Farook's relatives had no idea why the couple burst into a holiday luncheon for Farook's co-workers and viciously opened fire, family lawyers said. Nor did they have an idea the couple had a makeshift bomb lab in the apartment they shared with their 6-month-old daughter and Farook's mother. Nor did they know either of them were radicalized.
"It just doesn't make sense for these two to be able to act like some kind of Bonnie and Clyde or something," Farook family attorney David S. Chesley told CNN's Chris Cuomo. "It's just ridiculous. It doesn't add up."
Officials: Farook talked to person investigated for terror
Neither Farook nor his wife had gotten into trouble with the law, according to police. And neither was on any list of potentially radicalized people.
But it's not known what connections Malik, who was born and raised in Pakistan and moved to Saudi Arabia around the age of 19, had with any terrorists or groups before the San Bernardino massacre.
Investigators are exploring Farook's communications with at least one person who was being investigated for possible terror connections. Some were by phone, some on social media.
"These appear to be soft connections," an official said, meaning they were not frequent contacts. Farook's last communication with the contacts was months ago.
The FBI wants to interview some of them to learn more about their conversations with Farook.
A federal official said Farook has "overseas communications and associations," but it's not yet clear how relevant they are to the shootings. "We don't know yet what they mean," the official said.
Family lawyer Mohammad Abuershaid said that Farook traveled twice to Saudi Arabia -- first in 2013 for the Hajj, the annual pilgrimage to Mecca that Muslims are required to take at least once in their lifetime, then again to marry Malik, whom he'd met through an online dating service.
FBI official David Bowdich said that he went to Pakistan as well, though Abuershaid denied that.
Farook and Malik "kept to themselves" in California, Abuershaid said. But the interactions they did have with relatives didn't hint at any significant changes in their thinking or demeanor, any turn to Islamist extremism, or any sign they were plotting a mass killing, according to the lawyer.
"There was nothing to show that (Malik) was extreme at all," Abuershaid said. "(And Farook) was a normal guy, in every sense of the word."
Did a workplace dispute boil over?
It's not that Farook's family denies the couple carried out this massacre. They are shocked by it. And they're also "very remorseful and they're very sad," Abuershaid said.
But that doesn't mean they can explain it. And the shooters didn't make it easy for authorities: The hard drive from their computer is gone, and two relatively new cell phones were found smashed in a garbage can near one of the crime scenes, law enforcement officials said.
Authorities haven't ruled out what President Barack Obama called "mixed motives," meaning that Islamic radicalism and workplace grievances both could have driven the attack.
San Bernardino Police Chief Jarrod Burguan has said there were indications Farook appeared angry when he suddenly left Wednesday's holiday luncheon at Inland Regional Center, only to return heavily armed.
The Farook family lawyers didn't speculate on his reasoning, though Chesley did say that "at some times co-workers have done silly things, like made fun of Syed's beard."
One of Farook's colleagues, Nicholas Thalasinos, liked to discuss religion and politics. He was one of the people killed in the Wednesday attack.
Farook and Thalasinos, reportedly a devout Messianic Jew, once had a "heated, passionate" discussion, said Kuuleme Stephens, a friend of Thalasinos, who had called him at work.
The men were sticking by their strongly held positions but were not fighting, Stephens said.
Thalasinos' widow, Jennifer, said he was very verbal about terrorism. "He's very upset about what ISIS has been doing and the radicalized Muslims," she said.
'Double life or ... really good at hiding'
No one -- not family members, no co-workers, not neighbors -- has said anything to suggest they saw this bloodbath coming.
Farook had been a regular at the Islamic Center of Riverside, California. That center's director, Mustafa Kuko, recalled him seeking advice about his new wife and her transition to America.
"He seemed like someone very genuine to establish a family on (a) good foundation," Kuko said.
Before Farook "kind of disappeared abruptly," the Islamic Center director knew him as "a quiet person. He looked like someone who is peaceful. ... He was nice."
A mob of reporters was allowed inside Farook and Malik's rented Redlands townhouse Friday, getting a glimpse at how they lived. Much of it appeared relatively mundane -- from a hanging clock to couches to many thing for the couple's young baby like a crib, ExerSaucer and other toys.
But there were also hints of something more, like shattered glass, boarded-up windows and lists of items seized by federal authorities.
Even those who knew Farook best didn't see anything to suggest something nefarious, according to family representatives.
That included Farook's mother, who thought nothing of it when the pair had her watch their 6-month-old girl while they went to a doctor's appointment, Abuershaid said. The lawyer didn't know if there ever was a doctor's appointment -- only that the mother initially worried that Farook had gotten shot, not that he was doing the shooting.
Chesley expressed surprise that Malik, whom he described as being "about 90 pounds, so it's unlikely she could even carry a weapon or wear some type of a vest or do any of this," could have been an active participant in the horror.
"There were no signs, no warnings, that Syed Farook and his wife were taking that path," the head of the Council of Islamic-American Relations' Southern California branch, Hussam Ayloush, told CNN on Friday.
"It seemed that either they had a double life, or they were really good at hiding what seems to be their new ideology or their intentions."