One of the two people accused of killing 14 at a holiday party in California apparently pledged allegiance to a leader of Islamic State militant group, two U.S. government sources said on Friday, reports Reuters.

Tashfeen Malik, 27, and her husband, Syed Rizwan Farook, 28, were killed in a shootout with police hours after the Wednesday massacre at the Inland Regional Center social services agency in San Bernardino, about 60 miles (100 km) east of Los Angeles. The attack was the deadliest mass shooting the United States has experienced in three years.

U.S. investigators are evaluating evidence that Malik, a Pakistani native who had been living in Saudi Arabia when she married Farook, had pledged allegiance to Islamic State leader Abu Bakr al-Baghdadi, two U.S. officials told Reuters. They said the finding, if confirmed, could be a "game changer" in the investigation.

Pakistani intelligence officials have contacted Malik's family in her homeland as part of the investigation, a family member said.