As new details emerge about the San Bernardino attackers, one source has located a photo of the future terrorists entering the U.S. for the first time.

ABC News obtained a picture of Tashfeen Malik and Syed Rizwan Farook passing through customs in Chicago's O'Hare International Airport on July 27, 2014. Malik, covered in a black hijab, looks directly into the camera with her husband staring blank-faced behind her.

According to U.S. officials, Chicago native Farook traveled to Saudi Arabia in July 2014, returning with Malik less than two weeks later. The Pakistani-born woman was able to enter the country on a "fiancé" visa.

Investigators have now determined that the San Bernardino office party attack that left 14 dead and 21 wounded was an act of terrorism, perpetrated by the radicalized Malik and Farook.

"The investigation so far has developed indications of radicalization by the killers, and of potential inspiration by foreign terrorist organizations," FBI director James B. Comey said at a news conference in Washington, according to The New York Times.

Comey went on to say that investigators had not found evidence that the couple were directly connected to a larger terrorist group or cell.

The Islamic State terror group declared the two attackers to be followers of their cause during an online radio broadcast Saturday.

Malik also announced her allegiance to ISIS on Facebook around the time of the shooting, a Facebook spokesman said.

Although it is uncertain if the attack was premeditated, the victims were not random. They were all former colleagues of Farook, throwing a party for the San Bernardino County Department of Public Health. Sources say Farook became agitated at the party and left. Several minutes later, he returned with his wife, wearing masks and tactical gear, and armed with handguns and assault rifles.

The couple were eventually gunned down by police as they tried to make their escape.

The FBI is continuing to investigate the attack and have reportedly set their sights on Farook's father. The elder Syed Farook, 66, spent extensive time in Pakistan. He has been added to the FBI's terrorist watch list.