RIVERSIDE, Calif. -- The gunman who killed his co-workers in San Bernardino, California, and the friend who bought the assault rifles used in the shooting were related through marriage and may have plotted an attack together three years ago.
New revelations from officials and public records show a much deeper connection between Syed Rizwan Farook and Enrique Marquez than previously was disclosed. Marquez has not been charged with a crime.
Marquez purchased high-powered weapons at least three years ago that Farook and his wife used to open fire on a holiday gathering of Farook's fellow health inspectors Dec. 2, killing 14 people.
The ATF says the FBI is currently asking Marquez about how and why he purchased the AR-15 style weapons he transferred to Farook, reports CBS News' Paula Reid. The FBI has not released the information from these interviews, but at this point the ATF believes the AR-15 style weapons were purchased legally by Marquez.
The FBI is taking a closer look at whether the transfer was legal. The FBI is asking Marquez whether he purposefully bought the guns for himself or for Farook. If it turns out he purchased them in his own name, knowing he would transfer them to Farook, then that would be a crime.
CBS News has learned that the FBI is searching a lake near the San Bernardino shooting -- looking for a hard drive missing from the Farook home.
The FBI has said that Farook's wife declared her allegiance to the Islamic State of Iraq and Syria (ISIS) group in a Facebook posting shortly before the attack.
Farook, 28, and his wife, Tashfeen Malik, 29, were killed hours later in a shootout with police, leaving behind a 6-month-old daughter.
A custody hearing for the 6-month-old was held Monday, with the sister of Farook seeking to adopt the baby, the Council on American-Islamic Relations said.
No long-term decisions were made, and the child will remain in county custody for now. Another hearing is set for next month.
"The family is naturally distraught at the separation and are eagerly awaiting to obtain custody of the six-month-old girl," CAIR said in a statement.
"I can never imagine my brother or my sister-in-law doing something like this, especially because they were happily married, they had a beautiful 6-month-old daughter," Farook's sister Saira Khan told CBS News' David Begnaud in an exclusive interview last week. "It's just mind boggling why they would do something like this."
FBI Director James Comey told the Senate Judiciary Committee on Wednesday that the two shooters were radicalized well before Malik came to the U.S. on a fiancée visa and they had discussed jihad and martyrdom as early as 2013.
Investigators are trying to determine if Farook's path toward extremism predated that time and whether it led to plans to launch an attack in 2012, according to two people familiar with the investigation who were not authorized to discuss the matter publicly and spoke on condition of anonymity.
Marquez and Farook "were plotting an actual attack" that year, including buying weapons, but became apprehensive and shelved the plan because of law enforcement activity and arrests in the area, said Idaho Sen. Jim Risch, a Republican who sits on the Senate Select Committee on Intelligence.
Marquez, 24, spoke with federal authorities after they raided his mother's Riverside house over the weekend. He and Farook were friends for years and became family last year with a sister-in-law in common.
The two men were listed as witnesses on the marriage license when Farook's brother, Raheel, wed a Russian woman in 2011.
Three years later, Raheel Farook and his wife, Tatiana, were witnesses to Marquez's marriage to her sister, Mariya Chernykh, according to Riverside County records.
The ceremony took place at the Islamic Society of Corona-Norco, according to the marriage license, though the mosque's facility manager denied it occurred there.
Azmi Hasan said Wednesday that he understood Marquez had converted to Islam but said he was not a member of that mosque. Marquez had only worshipped there three to four times over seven years, said Hasan, who had not seen him in about four years.
Marquez had a security guard license in California for several years, but it expired last year. He had worked at Wal-Mart since May but has since been fired, spokesman Brian Nick said.
He spoke of wanting to join the military, Viviana Ramirez, 23, a fellow student at Riverside Community College told the Los Angeles Times. His brother-in-law, Raheel Farook, is a Navy veteran who served from 2003 to 2007 and earned the Global War on Terrorism Expeditionary Medal and the Global War on Terrorism Service Medal, among other awards.
Marquez rarely spoke about his family or his marriage, Ramirez said.
Tommy Lopez, who said he became friends with Marquez after meeting at a punk rock show seven months ago, said he never talked about his wife and was not religious.
He last saw Marquez in the past month or so when Marquez fell asleep at a friend's house and they stacked beer cans on his body.
"When he woke up, he just started laughing," Lopez said. "He was a pretty laidback guy."
Right after the shooting, Marquez called his mother to say he was safe but that he wouldn't be coming home, neighbor Lorena Aguirre said. He later checked into a mental health facility. It's unclear where he is now.
Marquez and his wife listed their address on their marriage license at the same Corona home where Raheel and Tatiana Farook live.
The Russian sisters came to the United States on visas for work or study exchange programs, according to a federal official who requested anonymity. The official was familiar with the visas but not authorized to speak publicly.
The FBI has not tied any Farook family members to the San Bernardino attack.
Comey described Farook and Malik as examples of homegrown violent extremists who appear to have radicalized "in place," drawing a distinction between the California attack and the one last month in Paris that officials suspect involved planning and training in Syria.
He said the FBI did not yet know if Farook and Malik's marriage was arranged by a foreign extremist organization.
Malik's father, reached in Jiddah, Saudi Arabia, condemned his daughter's actions and said he is "very, very sad. ... I am in such pain that I cannot even describe it."
The father, Gulzar Ahmed Malik, has been a resident in the kingdom since the early 1980s, the Saudi Interior Ministry says. His daughter was from Pakistan but traveled to Saudi Arabia.
Earlier on Thursday, photos on Farook's phone prompted a bomb sweep of some California schools.
Farook reportedly had photos of a local California high school in his cell phone. School officials say the FBI was able recover photos of the exterior of Carter High School in Rialto.
Farook inspected schools as part of his job, but the school said it was unusual for him to keep photos of its exterior.
After last week's attack, police used bomb-sniffing dogs to search schools Farook had inspected as part of his job.