RIVERSIDE, Calif. (AP) -- The gunman who killed his co-workers in San Bernardino 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. Farook, 28, and his wife, Tashfeen Malik, 29, were killed hours later in a shootout with police, leaving behind a 6-month-old daughter.

An FBI dive team on Thursday searched a small, urban lake about 3 miles north of the shooting site, though it was unclear what they were looking for. The search is related to the investigation into the massacre, according to a law enforcement official who was briefed on the investigation but was not authorized to speak publicly.

FBI Director James Comey told the Senate Judiciary Committee a day earlier 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.

The bureau has said that Malik declared her allegiance to the Islamic State group in a Facebook posting shortly before the attack.

Investigators are trying to determine if Farook's path toward extremism predated 2013 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.