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(cnbc.com) The FBI said Friday it has taken the lead role in the investigation of the San Bernardino mass shootings, and that it would investigate the attack as an act of terrorism.

David Bowdich of the FBI's Los Angeles office told reporters Friday that investigators had uncovered "telephonic connections" between the two shooters and other subjects of the investigations. He said he did not know if the couple had been directed by a larger terror organization, but "we are looking very carefully into that."

Still, he cited a number of pieces of evidence that pushed the agency to officially declare a terrorism investigation.

With a young wife, infant daughter and government job, Syed Farook appeared to have arrived at a sweet-spot in life. Friends knew the 28-year-old by his quick smile, his devotion to his Muslim religion and earnest talk about cars he would restore.

They didn't know the man authorities say was busy with his wife, Tashfeen Malik, building homemade bombs and stockpiling thousands of rounds of ammunition for a commando-style assault Wednesday on a holiday party of his co-workers that killed 14 and injured 21.

Malik, for her part, had posted a statement of support for ISIS leader Abu Bakr al-Baghdadi online "just before the attack," a law enforcement official told NBC News.

A Facebook executive told The Associated Press that Malik posted the material under an alias account at 11 a.m. Wednesday. That was about the time the first 911 calls came in and when the couple were believed to have stormed into the San Bernardino social service center and opened fire.

The executive spoke on condition of anonymity because this person was not allowed under corporate policy to be quoted by name. The company discovered the Facebook account Thursday. It removed the profile from public view and reported its contents to law enforcement.

Despite this find, authorities looking into the shooters have found no evidence in the couple's house to suggest any substantive connection to a foreign terror organization, a U.S. government source told Reuters.

Bowdich said he was aware of the post, but declined to comment on it further. Authorities said they continue to look for the details of the killers' motive.

A man who knew Farook from his mosque said he had trouble understanding the events.

"This was a person who was successful, who had a good job, a good income, a wife and a family. What was he missing in his life?" asked Nizaam Ali.

As authorities identified the dead and details about Farook's life began to take shape, the question of what motivated the slaughter remained unanswered. A U.S. intelligence official said Farook had been in contact with known Islamic extremists on social media.

Still, there is no evidence to suggest that ISIS "even knew" who the shooters were, a government source told Reuters.

Farook had no criminal record and was not under scrutiny by local or federal law enforcement before the attacks.

Authorities say that the couple sprayed as many as 75 rounds at the Inland Regional Center in San Bernardino before fleeing. They died four hours later and two miles away during a furious gunbattle with police.

The pair had more than 1,600 bullets when they were killed. Police said they also had 12 pipe bombs, tools to make more explosives, and more than 3,000 rounds of ammunition at home.

The FBI's Bowdich said it was "certainly a possibility" that the shooters were planning a second attack.

Read more here: FBI: Investigating Calif massacre as 'act of terrorism'