"Normal" is the word that people who knew the couple used to describe them before they murdered 14 people.
At least one parent -- Farook's father -- apparently knew about the radicalization, so why didn't he alert authorities?
Last weekend, the father, whose name also is Syed Farook, told an Italian newspaper that his son supported ISIS's ideology of establishing an Islamic caliphate.
"He said he shared the ideology of [ISIS leader Abu Bakr] al-Baghdadi to create an Islamic state, and he was fixated on Israel," La Stampa newspaper quoted the elder Farook as saying.
David Chesley, an attorney representing the family, told CNN that the father was on medications and didn't recall making those comments.
Other relatives in the United States didn't notice anything they thought was alarming about the couple, Chelsey said.
"The family was completely surprised and devastated. ... No one had any knowledge. If anybody would have, they definitely would have done something to stop it," Chesley told CNN's "Erin Burnett: OutFront" on Monday.
Farook's mother lived in an isolated part of the residence the couple rented, Chesley said. On the day of the attack, the couple left their baby with her.
Inside that residence in Redlands, a city that neighbors San Bernardino, authorities found pipe sections and hundreds of tools that could be used to make IEDs or pipe bombs, along with thousands of rounds of ammunition, according to San Bernardino police Chief Jarrod Burguan and the FBI.
How much, if anything, did Farook's mother know about the couple's plans? That's another question that remains unanswered. "Obviously, it's something that we're looking at very, very closely," U.S. Attorney General Loretta Lynch said Sunday on NBC's "Meet the Press."
How long did they believe terror was the answer?
On Tuesday, two U.S. officials told CNN there are indications the couple were on the path to believing terrorism was the answer before the Islamic State terror group declared itself to be a caliphate in June 2014.
The latest information raises the possibility that she was influenced other groups or individuals besides ISIS.
Earlier, investigators said that Malik had posted a message on Facebook -- under a different name -- just before the San Bernardino massacre pledging allegiance to al-Baghdadi, the ISIS leader. The exact language of her post wasn't released. Facebook says they took down the post the day after the shootings.
Were they looking for a group to join?
Was Malik radical and looking for a group to join? Was she also influenced by various terror groups? Was it she who influenced her husband or the other way around?
Sources tell CNN that there's no information to suggest that a foreign terrorist organization directed Malik and her husband. A senior law enforcement official said this week that Farook attempted to contact al-Nusra and Al-Shabaab but didn't say when or how those attempts were made. Al-Nusra, sometimes called al Qaeda in Syria, is a Sunni Islamist militia that is warring against the Syrian government in that country's civil war. Al-Shabaab is al Qaeda's terror outfit in Somalia.
Sources tell CNN that there's no information to suggest that a foreign terrorist organization directed Malik and her husband or that they are part of an organized group.
Supporters, martyrs, members of ISIS?
Were there any direct ISIS ties? Did the couple ever meet in person with anyone in ISIS? Did they take any direct orders from anyone in ISIS?
Three days after the San Bernardino attack, a recorded message from ISIS appeared on an online radio channel in Iraq. "We pray to God to accept them as martyrs," it said. The terror group has also called them "supporters."
ISIS, when claiming responsibility for other terrorist attacks, would call attackers "knights" or "soldiers" rather than supporters. "What they're calling these two are supporters, which is kind of a lesser level," indicating it might not have had direct contact with the couple, said retired Lt. Col. Rick Francona, a military analyst.
What do we know about their planning?
The evidence indicates that they planned, but for how long and for what scope of violence? They trained, but did anyone help them with the understanding that Malik and Farook would hurt people? Did they receive any funding to help them prepare, and who or what organization aided them financially?
The couple went to target practice
at gun ranges in the Los Angeles area, and two U.S. officials tell CNN that Malik seemed to be proficient with an AR-15 rifle, the kind of gun she used to shoot victims at Inland Regional Center in San Bernardino.
After attacking at Inland, the couple was able to take off in a black SUV, a move that also indicates planning, but even more alarming was that they didn't just speed out of town, they went back to their neighborhood. Why? Were they planning another attack? An answer remains elusive.
Investigators have also said that their process is slowed because Malik and Farook tried to destroy their electronics, but the FBI has still been able to glean some information from those items. "They covered their tracks pretty well," a U.S. official told CNN.
What clues from their lives in the U.S.?
A working theory among investigators is that Malik was radicalized prior to meeting her husband, who is a U.S. citizen. Like her husband, Malik wasn't on any list of potentially radicalized people, and there was no evidence linking her to any terror groups overseas prior to news of the Facebook posting. She appeared to be a Muslim like any other -- praying and fasting.
Malik was born and raised in Pakistan and lived in Saudi Arabia before coming to the United States on a fiancée visa. She later became a lawful permanent resident. Mohammad Abuershaid, an attorney for Farook's family, said Malik moved to Riyadh when she was between 18 and 20. Abuershaid said the couple met through an online dating website and connected in person when Farook traveled to Saudi Arabia in 2013 during the Hajj pilgrimage.
Mustafa Kuko, director of Islamic Center of Riverside, counseled Farook as he was looking for a religious woman to marry, Kuko said. Farook married Malik in a religious marital ceremony during a second trip to Saudi Arabia a short time later, and then returned the U.S. with his new wife, Kuko said.
It was on Farook's second return trip from Saudi Arabia that Malik entered the United States, said Kuko, who officiated the couple's U.S. marital ceremony at his mosque in 2014.
"She was very conservative. She was a stay-at-home mom," Abuershaid said.
Farook, who attended California State University Fullerton, was an environmental health specialist with the San Bernardino County health department, where he'd worked for five years. Records indicate he made $53,000 in 2013.
Law enforcement officials told CNN that Farook had been in touch via phone and social media with at least one person whom the FBI suspected of international terrorism. They wouldn't elaborate.
What clues lie in their past abroad?
A security source said authorities have raided Malik's father's home
in Multan, in central Pakistan, a country that has long been central in the war on terror
. It borders Afghanistan, where the U.S. has been at war for 14 years, and is one of the countries in which the U.S. has conducted drone strikes.
Police and a friend of Malik said the San Bernardino shooter was in Pakistan until spring 2014, right around the time she got married. The father's home was padlocked and chained shut when Monday's raid was carried out. Police seized religious instruction books, audio CDs with Quran readings and various documents, according to Pakistani intelligence sources.
Malik took but never completed a Quranic course through the Al-Huda International Welfare Foundation. In a statement, that religious study center said that she told her instructor in May 2014 that she wouldn't be able to finish because she was about to get married.
And Abdul Aziz, the main cleric of the Red Mosque in Islamabad, Pakistan's, "denied any link or connection" to Malik and denied that he'd had pictures taken with her.
Was the attack related at all to Syed's job?
Investigators are considering that the couple's violence also had something to do with experiences Syed had at work.
So far there haven't been any friends of the couple who have spoken out, but co-workers Patrick Baccari and Christian Nwadike told the Los Angeles Times
that Farook was quiet and rarely started a conversation. He was a devout Muslim, they said, but he didn't talk about religion at work. Another co-worker, Griselda Reisinger, told the newspaper that Farook never struck her as a "fanatic."
Co-worker Jennifer Kosse told CNN that she knew Syed.
"There's no way I would have thought that he would ever do that," she said, adding that she did not know Malik.
David Chesley, an attorney representing Farook's family, told reporters that Farook was "an isolated man" and that co-workers made fun of his beard.