On Wednesday morning, Syed Rizwan Farook, 28, and Tashfeen Malik, 27, dropped off their six-month-old baby with Farook's mother, saying they were going to a doctor's appointment.
By noon, according to police, the couple had donned assault clothing, armed themselves with rifles and stormed a holiday party attended by San Bernardino County employees, killing 14 people and wounding 17 others.
Before sunset, after a shootout with police, they were both dead, leaving a grieving community with few clues to puzzle out the motive for the carnage.
Syed Farook, born in the United States, worked as an environmental health specialist for San Bernardino County, inspecting restaurants for health violations, according to authorities and a website that tracks public employees. As part of his job, he also inspected public pools at locations including apartment and senior housing complexes and country clubs. Records show him performing these duties as recently as July.
On Wednesday, he attended the annual holiday gathering for employees of his department, but then left, returning later with weaponry and Malik.
San Bernardino Police Chief Jarrod Burguan said that the shooting spree had clearly been planned in advance and that the suspects left several explosive devices, which appeared to be pipe bombs, at the scene of the massacre.
SueAnn Chapman, a cashier and waitress at China Doll Fast Food, a restaurant that Syed Farook inspected earlier this year for his job with the county, said he didn't seem unusual when he turned up.
"He was real quiet," Chapman said. "He checked the food and said he was here because somebody complained. ... He looked completely normal."
Burguan said he did not know whether Farook and Malik were wed, but officials with the Council on American-Islamic Relations (CAIR) who had been in touch with the family said they were husband and wife.
The couple were married for two years and have a six-month-old baby girl, Hussam Ayloush, executive director of the Los Angeles chapter of CAIR, told Reuters.
The couple left the baby with Farook's mother in the nearby city of Redlands early on Wednesday morning, Ayloush said, relaying information he got from the brother-in-law of Farook. They told her they were going to attend a doctor's appointment for the wife.
Burguan said that police investigating the shooting went to a house in Redlands on Wednesday afternoon, and saw the couple take off in a black SUV. Police pursued the car to San Bernardino, where the gun battle ensued that left Farook and Malik dead.
Farook's family was originally from South Asia, while Malik was believed to be from Pakistan and had lived in Saudi Arabia before coming to the United States, Ayloush said. Farook had an older brother, he added, who had served in the U.S. military.
Public records suggest possible turbulence in Farook's younger life.
In 2006, Rafia Farook, who records indicate is Farook's mother, filed in a Riverside court for divorce from her husband, also named Syed Farook.
She enumerated multiple instances of domestic abuse in the legal filing, and said her husband "threatens to kill himself on a daily basis." During one incident, she said in a court filing, her son came between them "to save me."