This is last picture taken of Syed Farook before he and his wife went on a rampage at his work's holiday party - killing 14 people and injuring 22 more in a religiously-motivated attack.

In the photo, Farook looks serious as he poses with four other beaming co-workers wearing and holding up festive props in front of a Christmas tree at the Inland Regional Center in San Bernardino, California last December 2.

Farook would later leave the party early, only to return with his Pakistani-born wife and open fire on dozens of his co-workers.

Syed Farook, right, refuses to smile as he poses with his co-workers at a holiday party

Farook's last photo was taken just before he and his wife went on their brutal rampage

Authorities now believe that Muslim Farook and his wife Tashfeen Malik, left, were upset he had to attend a holiday party steeped in Christian tradition

After the attack, the couple made a pledge to ISIS online, but investigators believe the attack may have been inspired by a more personal vendetta against Farook's bosses at the health department.

Investigators have obtained emails written by Malik, in which she complains that her husband shouldn't have to attend a mandatory Christmas party if he is Muslim, according to ABC reports.

'She had essentially made the statement in an online account that she didn’t think that a Muslim should have to participate in a non-Muslim holiday or event,' San Bernardino police chief Jarrod Burguan said.

'That really is one over the very, very few pieces of potential evidence that we have that we can truly point to and say, "That probably is a motive in this case."'

Farook attended a mandatory training session at the Inland Regional Center on December 2, 2015, that was to be followed by a company holiday party

The couple initially escaped but were shot dead in a shootout with police just four fours later

Above, the pistols and assault rifles the couple used in the attack last year which left 14 dead and 22 injured

It's still unclear when they started preparing for the attack. Surveillance footage shows Farook practicing to shoot a pistol and an assault rifle at a local firing range just two days before the attack.

The husband-and-wife terrorists returned to the holiday party equipped with assault rifles, leaving those inside mostly helpless to run and hide.

Police were quick to arrive on the scene but by then, Farook and Malik had already fled in their black SUV.

Surveillance footage even shows them making a U-turn outside the center and driving calmly past emergency vehicles rushing to the scene with lights and sirens blazing.

A composite photo of all 14 victims from the San Bernardino shooting rampage. They are top row left: Robert Adams, Isaac Amanios, Bennetta Betbadal, Harry Bowman and Sierra Clayborn. Second row from left: Juan Espinoza, Aurora Godoy, Shannon Johnson, Larry Daniel Kaufman and Damian Meins. Bottom row from left: Tin Nguyen, Nicholas Thalasinos, Yvette Velasco and Michael Wetzel

For the next several hours, the couple never went farther than seven miles from the center, and even drove right by police barricades around the center according to CCTV footage. It's now believed that the couple were returning to the scene so that they could remotely set off bombs they left behind in the building.

Police officers found them driving around in the area four hours later and tried to stop the couple. They then got into a shootout with police and both were killed.