In an online radio broadcast Saturday by the Islamic State, the group said that two “supporters” had carried out the attacks in San Bernardino but stopped short of referring to the couple as members. The group praised the attacks but didn’t claim responsibility for it, according to the Associated Press.

The FBI said Friday that it is investigating the San Bernardino, Calif., massacre as an act of terrorism, with officials revealing that the Pakistani woman who teamed with her husband in the slaughter went on Facebook afterward to pledge her allegiance to the leader of the Islamic State.

Investigators are trying to determine if the husband-and-wife killers acted alone — inspired, but not directed, by foreign Islamist radicals — or were involved in a more elaborate plot.

Hundreds of federal agents, in the United States and overseas, are looking for any contacts that the shooters — Chicago-born Syed Rizwan Farook, 29, and his wife, Tashfeen Malik, 27 — might have had with terrorist groups.

“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 Friday. But he said that, so far, there is no evidence that they were part of a larger group.

There are a host of unknowns in this case, including whether the shooters had other targets in mind, a possibility suggested by the dozen pipe bombs and the thousands of rounds of ammunition in their apartment.

The shooters also sought to cover their tracks by damaging some of their personal electronic devices. Authorities found two crushed cellphones near the apartment and were examining other evidence that the shooters “attempted to destroy their digital fingerprints,” said David Bow­dich, assistant director in charge of the FBI’s Los Angeles office.

Farook and Malik were slain by police in a frenzied gun battle four hours after they killed 14 people and wounded 21 in an attack Wednesday at a gathering of county workers. For two days, FBI officials — as well as President Obama — had expressed uncertainty about whether the rampage at the Inland Regional Center was terrorism or an unusual case of workplace violence.

But new evidence pointed to an ideological motivation rather than a workplace grudge. Law enforcement officials said that, after the shooting, Malik went on Facebook and pledged her allegiance to Abu Bakr al-Baghdadi, the leader of the Islamic State, the militant group that says it has established a caliphate in Syria and Iraq.

A Facebook official confirmed the posting, speaking on the condition of anonymity because of the ongoing investigation. The official said Facebook, which is cooperating with law enforcement, identified and removed the post a day after the attack, saying any content praising an Islamic State leader violates its community standards.

‘A very, very private person’

Two criminal defense lawyers representing Farook’s mother, three siblings and brother-in-law held a news conference Friday and offered insight into the shooters, describing the husband as a loner and the wife as extremely conservative religiously, so much so that she would not be in the same room as her male in-laws. Malik’s brother-in-law had never seen her face.

“She did maintain certain traditions in terms of prayer and fasting. She chose not to drive voluntarily. She was a very, very private person. She kept herself pretty well isolated,” family lawyer David Chesley said.

Family and friends remembered the 14 victims of the Dec. 2 shooting attack in San Bernardino, Calif., as "hard-working, family-loving, gentle people." All but one worked for the San Bernardino County Department of Public Health with attacker Syed Rizwan Farook. (Jenny Starrs/The Washington Post)

“Syed didn’t want any fathers or brothers or brothers-in-law in the same room when she would also be there,” said another family lawyer, Mohammad Abuershaid.

“The family was not that close to him,” he added. “He was kind of like the lone wolf.”

A professor at Bahauddin Zakariya University in Multan, Pakistan, remembered Malik as a student.

“She used to wear complete veil and a religious-minded student,” Nisar Ahmad said by phone. “She was not mixing with her male class fellows in the department. ... But no one had the idea that she would act that as she never involved in such activities.”

Ghulam Shabir, director of public relations for the university, told The Washington Post that he was unaware of Malik’s attendance. He said a statement would be issued Monday after the university had a chance to check its records.

Lawyers emphasized that there are no established links between Farook, Malik and terrorist organizations, and Chesley said it is inappropriate to assign culpability to Muslims broadly when someone who is Muslim is involved in a shooting.

Farook and Malik were married in Riverside, Calif., in August 2014, according to the Riverside county clerk’s office. They had a daughter, born May 21 of this year. The baby is in child protective services, the lawyers said. They said they think they won’t be able to get her to family members — the child may be adopted by an aunt — until at least Monday, when there is a court hearing.

In one of the more bizarre moments in the case, the landlord for Farook and Malik allowed camera crews to enter the couple’s apartment Friday and film reporters rummaging through the family’s personal belongings, including photographs, toys and stuffed animals in the baby’s crib. The FBI said later that the agency had finished processing the crime scene and no longer had control over the apartment.

A friend of Farook, Gasser Shehata, said he used to see Farook two or three times a week for prayer at the Dar Al Uloom Al Islamiyah-Amer mosque in San Bernardino. Shehata, an Egyptian by birth, said he talked with Farook soon after a Russian jetliner was destroyed over the Sinai Peninsula by a bomb in late October. The Islamic State claimed responsibility.

“I asked why they’re killing innocent people,” Shehata said. Farook didn’t say anything in response, he said.

Shehata said he thinks that if Farook had become radicalized by that point, he would have said something to indicate such views.

Three weeks ago — just before the terrorist attacks in Paris — Farook stopped coming to the mosque, he said.

Farook had maintained a Facebook page that was deleted before the shooting, according to Rita Katz, executive director of the SITE Intelligence Group, which tracks online communications of extremists. A post on an Islamic State-linked blog Friday claimed that the attack was carried out by Islamic State supporters, SITE reported.

But although the Islamic State quickly asserted responsibility for last month’s shootings in Paris and for other recent attacks, the group so far does not appear to have done the same for the San Bernardino shooting.

‘This is not Jihad 101’

At the shooters’ apartment, police recovered four guns, including two assault rifles. Comey said Friday that investigators had located the individual who bought the two rifles and had cleared the person of any involvement in the attack.

Investigators said the couple had managed to stay off the FBI’s radar. There is no evidence that they tried to make contact with Islamic State operatives overseas.

“This is not Jihad 101,” a senior law enforcement official said, noting that the shooters had not taken steps commonly seen in previous terrorist attacks, such as attempting to make contact with Islamic State militants or sharing the group’s propaganda.

The Islamic State uses sophisticated propaganda to recruit adherents and has called for lone-wolf attacks in the United States and other countries.

In Saudi Arabia, intelligence agencies are investigating Malik’s time in that country. The Saudi government has not confirmed when she lived there or whether she left with Farook when he visited for nine days in the early summer of 2014.

A Saudi official said that Malik’s name does not appear on any watchlist there and that no evidence has been uncovered of contacts between her and any radical individual or group during her time there. The official said Malik had lived with her father “off and on” in Saudi Arabia over the years, apparently traveling back and forth an undetermined number of times to Pakistan, her country of birth.

A senior law enforcement official said Friday that the attack in San Bernardino evoked the mass shooting in Chattanooga, Tenn., earlier this year, when ­24-year-old Mohammad Youssef Abdulazeez opened fire at an armed-forces recruiting center and a Navy Reserve center, killing five people. In that case, the official pointed out, it took days for the FBI to sort out what had happened, and some questions remain unanswered.

Some evidence collected in California was flown across the country Thursday so the FBI could examine it in its lab, Bowdich said.

The FBI’s Operational Technology Division in Quantico, Va., has units that can try to retrieve data from smashed, burned and damaged devices, including cellphones, hard drives and flash drives. A computer analysis team there can try to pull call records, pictures, GPS location data, address book information and other data from the devices, while a forensic analysis unit can attempt to restore and enhance audio and visual data.

In the meantime, the FBI said Americans should be alert but not panicked about the threat of further terrorist attacks.

“Do not let fear become disabling,” Comey said. “Please channel that sense of fear into something healthy. Just an awareness of your surroundings.”

William Dauber, Abby Philip, Thomas Gibbons-Neff, Missy Ryan and Eli Saslow in San Bernardino; Tim Craig in Islamabad, Pakistan; and Karen DeYoung, Sarah Larimer, Ellen Nakashima, Greg Miller, Brian Murphy, Niraj Chokshi, Sari Horwitz, Elahe Izadi, Wesley Lowery, Kevin Sullivan, Julie Tate and Alice Crites in Washington contributed to this report.