San Bernardino shooter had planned another attack in 2012
CNN, citing top officials, said Farook and another person conspired in 2012 to attack a "specific target."
However, they abandoned the plan following a police anti-terror operation, which resulted in several arrests in the area in southern California where they lived.
On Tuesday, the FBI claimed Farook and his Pakistani wife Tashfeen Malik were radicalized for a considerable time.
Sources from the investigation added Farook and Malik had received $28,000 through the internet around two weeks before the shooting.
The San Bernardino shooting on Dec. 2, killed 14 people and injured 21 wounded, and is being regarded as one of the worst terrorist attacks on U.S. soil since 9/11.
Jihadist group Islamic State claimed the shooters were their followers.