The man who purchased two assault rifles used in last week’s shooting in Southern California was not only gunman Syed Rizwan Farook’s neighbor, but also a relative, media reports said Wednesday. The news comes as FBI agents continue to investigate the motive behind the San Bernardino, California, attack.

Enrique Marquez, who legally bought the weapons at least three years ago, had a sister-in-law in common with Farook, according to marriage records, cited by the Associated Press (AP). Marquez and Farook were friends for a long time and became relatives last year after Marquez married that woman's sister. On Dec. 2, Farook and his wife, Tashfeen Malik, opened fire at the Inland Regional Center, killing 14 people and injuring 20 others.

Marquez revealed during questioning that he and Farook had planned an attack in the United States in 2012 but later dropped the plot, according to one law enforcement official briefed on the investigation. This was confirmed by Idaho Sen. Jim Risch, a Republican who sits on the Senate Select Committee on Intelligence, the AP reported. 

Marquez and Farook "were plotting an actual attack" in 2012, including purchasing weapons, but became apprehensive and put their plans aside after some law enforcement activity and arrests in the area they planned to target, Risch reportedly said.

Marquez, the neighbor of Farook, had worked at Wal-Mart since May but has since been fired, and was listed as a witness on the marriage license when Farook's brother, Raheel Farook, married in 2011, according to documents. In 2014, Raheel and his wife, Tatiana Farook, were witnesses at Marquez's marriage to Mariya Chernykh, Tatiana's sister, according to Riverside County records.

Tatiana and Chernykh are both Russians, the AP reported, citing a federal official who spoke on condition of anonymity, adding that the two sisters came to the U.S. on visas for work or study exchange programs.

Since the San Bernardino attack, investigators have been digging into the lives of Syed Rizwan Farook and Malik, both of who did not come to the attention of law enforcement officials before the shootings.

On Wednesday, FBI Director James Comey reportedly described the two shooters as "homegrown violent extremists" who were radicalized and dedicated to jihad as early as the end of 2013 -- before they started dating online. Their radicalization began even before the Islamic State group, also known as ISIS, rose to prominence. The couple had pledged allegiance to the Sunni militant group, which now controls several parts of Iraq and Syria.