After the mass shooting in San Bernardino, Calif., on Dec. 2, that left 14 people dead, the FBI is unearthing more information about who was involved in the attack. Here's what we know about Syed Rizwan Farook, his wife Tashfeen Malik and his neighbor Enrique Marquez. (The Washington Post)

Syed Rizwan Farook was looking for a wife. On at least two online sites, he posted details for prospective brides. “Religious but modern,” he apparently wrote on one. He made a point of noting his American citizenship on another.

How he ultimately made contact with Pakistan-born Tashfeen Malik remains unclear. But family members said Farook traveled to Saudi Arabia, where Malik was living, and that they returned to Southern California as a couple and began a life in quiet Redlands, an area of ranch houses and once lush lawns now browned by drought.

Wednesday morning, they dropped off their 6-month-old daughter with Farook’s mother, according to family members. Sometime around midday, police say they donned masks and armed themselves with assault rifles and handguns before storming a holiday party hosted by the county health agency where Farook worked. At least 14 people died. Hours later, 28-year-old Farook and 27-year-old Malik were dead by police gunfire just two miles from the massacre site.

Details about the lives and views of the two suspected assailants are still incomplete. But as authorities stitch together the events surrounding the latest U.S. mass shooting, two disparate portraits emerge — one of American suburban stability and the other of immigrant reinvention — that seem to intersect somewhere in the Pakistani diaspora.

Also still puzzling investigators is what drove the two suspected attackers to turn the holiday party into a killing zone. It is extremely rare for a mass shooting in America to have multiple perpetrators — and even more so for one of them to be a woman.

“We have not ruled out terrorism,” said San Bernardino Police Chief Jarrod Burguan.

Hussam Ayloush, executive director of the Council on American-Islamic Relations in Los Angeles, told The Washington Post that Farook and Malik had been married for two years.

The couple told the grandmother that they had a doctor’s appointment and needed her to take care of the child, Ayloush said.

“I have no idea why he would do something like this,” Farhan Khan, who is married to Farook’s sister, said at a news conference held by CAIR late Wednesday night.

Farook — born in Illinois to Pakistani immigrant parents — was a San Bernardino County employee who had worked for five years as an environmental health specialist in the public health department, which was hosting the holiday party where the shooting occurred. According to state employee records, Farook’s total compensation in 2013, including salary and benefits, was $71,230.

Malik was born in Pakistan and spent time in Saudi Arabia before marrying Farook, said Ayloush, the Muslim community leader.

The California couple join a long roster of convicted and alleged mass shooters from recent years. But in contrast to many others, Farook and Malik do not appear so far to have left a digital trail that could point to their motives.

Christopher Harper-Mercer, the 26-year-old who fatally shot nine people and then killed himself at a community college in Oregon in October, left behind social media profiles that indicated an affinity with Nazism, anti-religious views and a desire to “lash out at society.”

Charleston, S.C., church shooting suspect Dylann Roof posted Facebook photos of himself wearing emblems of white supremacist movements, and owned a website containing a lengthy manifesto against racial minorities.

But where Farook and Malik are concerned, the traces of them that can be found on the Internet are relatively benign: a baby registry that appeared to be in Malik’s name, and undated online dating profiles that appeared to be Farook’s. Among other things, he stated an interest in target shooting.

The baby registry page cites a May due date in Riverside, which is near San Bernardino. Malik’s requests are modest: diapers, baby wash, swabs and a convertible car seat.

Another site — described as “for people with disabilities and second marriage” — includes a description that appears to match Farook.

The “About Him” section on the iMilap.com site introduces someone who works for the county as a “health, safety and envorimental [sic] inspector.” It further states that he is from a religious but modern family of four, lives with his parents and enjoys working on cars as well as “just hang out in back yard doing target pratice [sic] with younger sister and friends.”

He added that he enjoyed working on vintage and modern cars, and read religious books while enjoying eating out sometimes.

On another matchmaker site, Dubaimatrimonial.com, a person believed to be Farook described himself as having family roots in Karachi, noting he was born in Chicago and was residing in Los Angeles as an American citizen.

Farook graduated from California State University at San Bernardino with a degree in environmental health in 2009, according to the university’s commencement document.

His seemingly steady persona — high school, college, career — stands in contrast, however, with the apparently turbulent home life of his parents for more than a decade.

The couple, Rafia and Syed Farook, filed for Chapter 7 bankruptcy protection in 2002, according to county documents.

Four years later, Rafia then submitted paperwork for a separation after more than 24 years of marriage, citing verbal and physical harassment and describing her husband as “irresponsible, negligent, and an alcoholic.” Conditions were put in place for visitation with their daughter, Eba, who was born in 1991 — four years after her brother, the alleged shooter.

A series of court filings were made between 2006 and 2012 related to their separation. In one 2008 document, the hit from the U.S. financial crisis appeared to be noted: Showing the estimated value of their Riverside home at $175,000 but owing about $100,000 more. A judge granted her petition for a divorce earlier this year.

In interviews with the Los Angeles Times, Syed Farook’s co-workers in the public health department said he was “quiet and polite, with no obvious grudges.”

“He never struck me as a fanatic; he never struck me as suspicious,” Griselda Reisinger said.

Fellow inspectors Patrick Baccari and Christian Nwadike said the “tall, thin young man with a full beard” rarely started conversations, but he was well-liked and spent a lot of time in the field.

They said Farook was a devout Muslim but didn’t discuss religion at work.

Reports show that Farook inspected public pools and eating establishments. His job required him to check the cleanliness of food surfaces and cooling methods, analyze chlorine levels and test kitchen equipment.

Wednesday’s mass shooting was the deadliest in the United States since 2012, when a lone gunman killed 20 children and six adults at Sandy Hook Elementary School in Newtown, Conn.

According to CNN, of the 28 deadliest shootings in U.S. history before Wednesday, “only two have come at the hands of multiple shooters: the February 1983 killings at the Wah Mee gambling and social club in Seattle and the Columbine High School massacre in Littleton, Colorado, in 1999.”

An FBI report released last year said there were 160 “active shooter” incidents in the United States between 2000 and 2013. Among those, all but two involved a single shooter, the report states.

The exceptions, according to the FBI:

• On April 6, 2012, Jacob Carl England, 19, and Alvin Lee Watts, 32, each armed with a handgun, drove through the streets of Tulsa, Okla., firing their weapons, killing three people and wounding two others, according to the report.

• On Aug. 27, 2011, Tyrone Miller, 22, and an additional unidentified shooter(s), armed with handguns, allegedly began shooting at a house party in Queens, N.Y., according to the report. Miller was arrested two years later in North Carolina, but the unidentified suspect(s) remains at large.

The FBI’s definition excludes the D.C.-area sniper shootings, which began Oct. 2, 2002, when John Allen Muhammad and Lee Boyd Malvo began shooting Washington-area residents — a string of attacks that left 10 dead and three seriously wounded.

According to the FBI report: “Active shooter is a term used by law enforcement to describe a situation in which a shooting is in progress and an aspect of the crime may affect the protocols used in responding to and reacting at the scene of the incident. Unlike a defined crime, such as a murder or mass killing, the active aspect inherently implies that both law enforcement personnel and citizens have the potential to affect the outcome of the event based upon their responses.”

The agency’s report did not include active-shooter incidents from 1999, the year two students at Columbine High School killed 12 students and a teacher before turning their guns on themselves.

And one of the San Bernardino attackers was a woman, which makes the incident even more unusual: Among the 160 active-shooter incidents logged by the FBI, only six of the shooters were female, the report states.

“If you have a buddy, you’re probably less inclined to commit suicide and destroy your life, unless you have a cause,” said David Hemenway, professor of Health Policy at Harvard. “Columbine was pretty unusual. That was like Leopold and Loeb. Most of the time people who do this are just loners.”

Brian Murphy and Amy Brittain in Washington contributed to this report.

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The Calif. mass shooting was the second on Wednesday and the 355th this year