The last picture of Syed Farook shows him posing at his office Christmas party with colleagues before he killed 14 of them in San Bernardino.
US ABC News' investigative team discovered emails between Farook and his Pakistani wife, Tashfeen Malik, which indicate she was upset her Muslim husband was being forced to attend a Christmas gathering.
Not long after Farook was pictured in front of this Christmas tree, he killed 14 colleagues and injured 22 others.
"[Malik] 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 told ABC News.
"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'."