Fourteen people were killed in a gun attack on a holiday party in San Bernardino, California on Wednesday (Dec 2), the worst mass shooting in the United States since 2012.
The suspects - Syed Rizwan Farook, 28, and Tashfeen Malik, 29 - left their six-month-old daughter with his mother and went on the shooting rampage. Both were killed during a fierce shootout with police.
Here's what we know so far of the suspects and the investigation:
Who is Syed Rizwan Farook?
Farook is a US citizen born in Illinois to immigrant parents from Pakistan. He works as an environmental health specialist at the public health department in San Bernardino county and his job involves inspecting restaurants and swimming pools for health violations.
Those who know Farook said he is a devout Muslim who made a pilgrimage to Mecca in 2013 and prayed regularly at a mosque in Riverside, California and later at a mosque in nearby San Bernardino. Mr Mustafa Kuko, director of the Islamic Centre of Riverside, said he could not recall ever hearing Farook express extreme ideology. "He was a very quiet person, peaceful, never had an argument with anyone or a dispute," said Mr Kuko.
Farook's father, however, said in an interview with the Italian daily La Stampa that his son approved of the ideas of the Islamic State in Iraq and Syria (ISIS) and was fixated on Israel. “I always used to say to him, ‘Be calm, patience, in two years’ time Israel will no longer exist’,” he said in remarks reported in Italian.
Farook is found to have registered on at least three online dating sites. On ArabLounge.com, a site for Arab singles, he describes himself as single, Allah fearing, calm, thoughtful and simple. He says he is looking for a "girl who has the same outlook," who wears a hijab - the head covering worn in public by some Muslim women - and lives life to the fullest.
On iMilap.com site, he says he enjoys working on vintage and modern cars, reading religious books and eating out on occasion.
Farook met his wife Tashfeen Malik online and they married in Saudi Arabia.
Who is Tashfeen Malik?
Malik was born in Pakistan and lived in Saudi Arabia before she met Farook. She entered the US on a "fiancee visa" under a Pakistani passport.
She wears the niqab - a veil that covers the entire face except for the eyes - and Farook likes that, according to Mr Kuko.
Malik appears to have almost no online presence, with no visible profiles on Facebook, LinkedIn or other networking sites. But her name is stated in a gift registry for their baby hosted by the website TheBump.com. According to the registry, her baby was due on May 17. She has also signed up with the baby registry at Target store, asking for a car seat, baby wash, diapers and cotton swabs. All of the items are shown as purchased.
On the morning of Dec 2, Farook attended an annual holiday gathering for employees of his department held in a rented conference room at the Inland Regional Centre, which provides services for people with disabilities. But he left the party after a dispute, police said. He later returned to the party with Malik - both of them dressed in black assault-style clothing - and opened fire. "They came prepared to do what they did as though they were on a mission," said San Bernardino Police Chief Jarrod Burguan.
The couple sprayed the room with 65 to 70 rounds, killing 14 people and injuring 21 others, before fleeing the scene in a rented black sport utility vehicle. Police pursued the car and a gunbattle ensued that left Farook and Malik dead.
What has investigators found so far?
The Federal Bureau of Investigation (FBI) said the couple were radicalised for “quite some time” and both went for target practice at ranges around Los Angeles before the massacre. They apparently used their 6-month old baby as a mere “prop” to make themselves look like a happy American family.
Authorities, however, said there is no indication so far that the couple were part of an organised larger group or cell.
ISIS has praised them as “soldiers” of its self-proclaimed caliphate, while stopping short of claiming outright credit for the carnage.
What was found in their home?
The couple had two assault-style rifles, two semi-automatic handguns and 1,600 rounds of ammunition in their rented vehicle. At the townhouse which they leased in the nearby community of Redlands, police found another 4,500 rounds, 12 pipe bombs and bomb-making equipment.
The guns were legally purchased in the United States, said the Bureau of Alcohol, Tobacco, Firearms and Explosives. Farook bought the two handguns, while someone else bought the rifles.
Police also found flash drives, computers and cellphones in the townhouse.
SOURCES: REUTERS, AGENCE FRANCE-PRESSE, NEW YORK TIMES