SAN BERNARDINO, Calif. — As FBI divers continued to paddle the murky waters of a San Bernardino lake Saturday, the federal investigation into the massacre at a county health department party was reaching a critical juncture: Who were the two shooters talking to?

Officials have described Syed Rizwan Farook and his wife, Tashfeen Malik, as “self-radicalized terrorists” who killed 14 people in the Dec. 2 attack.

But federal law enforcement officials, speaking confidentially Friday and Saturday because the investigation is continuing, are also concerned that the two shooters were jointly or independently in direct contact with members of one or more foreign terror operations.

Whether Farook and Malik were ordered to carry out a terrorist attack, though, may well depend on what the divers bring up from the bottom of Seccombe Lake.

On Friday, undisclosed items were retrieved and the divers returned to the water Saturday in search of a computer hard drive and other electronic components. They are working on a tip that the shooters hurried to the lake and park area on the day of the attack and disposed of personal items there.

In addition, agents have recovered two smashed cellphones from a dumpster, and are examining those and other items from the couple’s Redlands home at the FBI’s crime lab in Quantico, Va.

In all, these items are surfacing as key pieces of evidence in what is hoped to eventually unravel the mystery behind the worst terror attack in the U.S. since Sept. 11, 2001.

At a Senate Judiciary Committee hearing this week, FBI Director James Comey was asked whether a foreign terror network arranged the couple’s introduction and eventual marriage in order for Malik, a Pakistani by birth related to radical Islamic militants, to enter the United States from Saudi Arabia after Farook, himself self-radicalized, combed the Internet and traveled abroad in search of a wife.

Evidence of involvement of a terror group in the San Bernardino plot would be a significant game-changer.

“Somebody had to put these two people together,” said one FBI source. “It’s a big world for them to just find each other.”

Farook and Malik were separately radicalized before they started courting and married, Comey testified. Farook escorted Malik to the U.S. in July 2014, two years after he allegedly discussed an earlier terrorist plot with a local friend. That friend, Enrique Marquez, has told investigators that he provided the couple with two semiautomatic assault rifles used in the San Bernardino attack, federal sources said.

Comey also has noted that the couple sent a joint digital message pledging their allegiance to the Islamic State on the day of the San Bernardino attack, either just before or after they entered the holiday meeting in camouflage with guns blazing.

Like the 9/11 hijackers who were recruited, trained and financed by foreign terror organizations, were Farook and Malik directed to carry out some kind of an assault before deciding on the Inland Regional Center and killing 14 people in San Bernardino? Or were they simply so caught up in the social media vitriol from such groups that, the couple acted on their own?

“At the least they were inspired to do this,” said one federal official. “At the worst, they were not only told to do something, but got help. We’re working toward the worst.”

Officials cautioned that it could take weeks or months to find an answer.

And the difference between inspiring and directing someone to act, the sources said, can often be a very fine line.

In the days before the 2009 attack at Fort Hood, Texas, Anwar al-Awlaki, a U.S. citizen turned al-Qaida recruiter, sent Army Maj. Nidal Hasan at least two direct emails. In the attack, Hasan shouted “Allahu Akbar!” as he killed 13 people.

Afterward, Awlaki posted on his blog, “Nidal Hasan Did the Right Thing.”

Hasan was sentenced to death; Awlaki was killed in a 2011 U.S. drone strike in Yemen.

Last May, two radicals from the Phoenix area attempted to storm a gathering of cartoonists drawing the Prophet Mohammed in Garland, Texas. They leaped from their car, firing semiautomatic weapons and wounding one security officer before they were killed.

One of the gunmen, Elton Simpson, had been in contact with an Islamic State recruiter known as Mujahid Miski, whose real name is Muhammed Abdullahi Hassan. He grew up in Minneapolis and moved to Somalia to reportedly join the Shabab terror group as a recruiter.

Shortly before the Garland attack, Simpson and Nadir Soofi pledged allegiance to “Amirul Mu’mineen,” or the “the leader of the faithful,” which authorities believe refers to the Islamic State leadership. After the incident, an Islamic State propagandist tweeted, “Allahu Akbar!!!! 2 of our brothers just opened fire.”

The two drove to Texas after Hassan reportedly posted a challenge encouraging radicals in the U.S. to follow the lead of two brothers who in January attacked the headquarters of the satirical magazine Charlie Hebdo in Paris, killing 12 people, including a police officer.

Simpson first tweeted a complaint about the upcoming cartoon contest in Texas. “When will they ever learn?” he asked.

Hassan allegedly responded, “The brothers from the Charlie Hebdo attack did their part. It’s time for brothers in the #US to do their part.”

Last month, Hassan turned himself into Somali authorities.

In a telephone interview with the Voice of America’s Somali Service, he said he has left Shabab and denied any involvement in San Bernardino.

“I don’t have anything to do with that attack or have any connections with those people,” he told the VOA. “I am not part of ISIS (Islamic State) and I have nothing to do with … any other jihadi movement.”

Hassan was indicted in Minnesota on suspicion of providing material support to a terrorist group and conspiring to kill people abroad. He also has a history of sending ominous computer messages encouraging “lone-wolf style” attacks.

It is exactly these kinds of social media communications that authorities are searching for in the San Bernardino case.

The officials said the FBI lab’s teams will probably be able to retrieve any erased communications the couple tried to hide by smashing phones or sinking a hard drive, and restore their digital past.