PHOTO: ABC NEWS

A year after the San Bernardino attack, FBI investigators are still seeking to answer key questions, including whether a mandatory Christmas party may have triggered the brutal shooting.Authorities are yet to determine the location of the married couple’s computer hard drive and whether assisted them in planning the attack. Authorities also believe that a mandatory Christmas party held at Farook’s workplace may have triggered the attack.A photo of Farook with his co-workers at the party is the last one taken of Syed Farook, just before he and his wife went on a rampage at the party - killing 14 people and injuring 22 more.In the photo, Farook can be seen with four other 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.According to ABC News, investigators have obtained emails written by Tafsheen Malik, in which she complains that her husband shouldn't have to attend a mandatory Christmas party if he is Muslim.“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.’”Authorities have said that US-born Farook and Malik, a native of Pakistan who lived most of her life in Saudi Arabia, were inspired by Islamic extremism. The couple, who were parents of a 6-month-old daughter, both died in a shootout with police four hours after the massacre.The Federal Bureau of Investigation is still seeking to determine if anyone assisted the couple, such as in financing the attack or helping to plan for it, FBI spokesperson Laura Eimiller said."While we have not charged anyone with providing support to Farook and Malik, we certainly will continue to investigate to determine if they were supported in any way," she said in a telephone interview.To that end, the FBI is still hoping to find the hard drive from the couple's computer, Eimiller said.A search by FBI divers in the weeks after the attack of a small lake at a park where Farook and Malik stopped in the hours after the shooting failed to turn up the hard drive.In addition, the FBI still has an 18-minute gap in accounting for the whereabouts of Farook and Malik in the hours they spent driving around San Bernardino in a sport utility vehicle after the attack at the city's Inland Regional Center.The couple left three pipe bombs at the center, in an apparent attempt to harm emergency workers caring for the wounded, according to authorities. The couple approached the center after the attack and might have been trying to detonate one of the devices remotely, Eimiller said.Several public events are scheduled for Friday in San Bernardino to mark the one-year anniversary of the attack.Elected officials and emergency responders who handled the attack will attend a ceremony at a San Bernardino blood bank on Friday morning. In the evening, another event is expected to draw at least 2,000 participants to an arena in the city.