Official: Neighbor Purportedly Bought 'Assault-Style' Weapons Used in San Bernardino Rampage

— -- An old neighbor of one of the San Bernardino shooters is believed to have purchased the “assault-style” rifles used in Wednesday’s massacre, a law enforcement official told ABC News today.

Overnight authorities raided the Riverside, California home of Enrique Marquez, who public records show lived next door to an old address of Syed Rizwan Farook, one of the San Bernardino killers, the official said. Police previously said that two handguns used in the attack were purchased by Farook and his wife-turned-accomplice Tashfeen Malik, but the other two guns – modified “assault-style” weapons -- had been purchased by an unidentified third party. The law enforcement official and a source close to the investigation told ABC News today the third party is suspected to be Marquez.

When ABC News visited the home linked to Marquez, a makeshift sign in the lawn said to keep off of the property.

The law enforcement news website TickleTheWire.com first reported Marquez as the alleged buyer. ABC News was unable to reach Marquez for comment for this report.

San Bernardino County Sheriff John McMahon told ABC News' Paula Faris this morning that federal officials knew the location of the man they believed purchased the weapons, but McMahon did not know if the man had been taken into custody. FBI Director James Comey said Friday that the gun purchaser was "not a suspect, at least at this point" in Wednesday's horrific attack.

Authorities previously said that all four weapons used in the attack were purchased legally.

ABC News' Jack Date contributed to this report.