One of the sources said Thursday that
Investigators have based that information on evidence left behind on Farook and Malik's computers and digital devices, not all of which the couple was able to destroy before they were killed in a firefight with police.
The timing of the rifle purchases is of great interest to
FBI Director James Comey also said this week that Farook was becoming self-radicalized around that time, and would soon meet Malik and escort her to the U.S.
FBI agents believe Farook abandoned his plans to launch an earlier attack after a law enforcement task force arrested three men in Chino in November 2012. The men were later convicted of charges related to providing material support to terrorists and plotting to kill Americans in Afghanistan. A fourth man arrested in Afghanistan was also convicted in the scheme.
It was Marquez who told FBI agents about Farook's earlier plans, according to one of the government sources who also requested anonymity.
The 24-year-old has waived his Miranda rights and been cooperative throughout marathon interviews with federal investigators, sources said.
"They were talking generally about something, but I don't think it made it to anything specific," one of the sources said of the earlier plot. "I don't think it got to a time or a place."
Marquez, a cycling enthusiast who wanted to join the U.S. Navy, was a longtime friend and neighbor of Farook's.
There was no paperwork transferring ownership of the weapons from Marquez to Farook, as required by law, government officials told The Times.
FBI divers were also searching a lake in downtown San Bernardino on Thursday in connection with the widening probe, but it was not clear what they were looking for, officials said.
Marquez's mother, Armida Chacon, addressed reporters on Thursday from her Tomlinson Avenue home in Riverside, sobbing as she said she hadn't been in contact with her son since the day Farook and Malik killed 14 people at the Inland Regional Center.
"I don't know how this happened .... My world is upside-down," she said. "My life changed Wednesday."
Chacon was outside with one of her sons, cleaning up the broken glass and twisted panels of their garage door. The damage occurred when federal agents raided the home over the weekend after Marquez became a central figure in the investigation.
As she combed through the wreckage of the garage door, Chacon eventually turned to the reporters camped out on the street and agreed to an interview if the cameras were turned off.
Marquez was his mother's "right hand at home," helping take care of his brothers, Chacon said.
She described him as a normal 24-year-old, who loved to hang out with friends and liked to go to parties.
"My son is a good person," she said.
When asked about Farook, Chacon said her son was friends with him, and "nothing more."
The government source said it remains unclear if Marquez had any involvement in the planning of the San Bernardino shooting or had any prior knowledge that an attack was pending.
Hours after the shooting, Marquez posted a cryptic message on his Facebook page.
"I'm. Very sorry sguys," the message read. "It was a pleasure."
He checked himself into a mental health facility. Marquez has told FBI agents that the Facebook post has become "misunderstood," according to one of the government sources.
Agents are also concerned that his mental and emotional state may affect what he has been telling interrogators, the source said.
While Marquez has been forthcoming about his ties to Farook, federal officials are still working to verify the information he has provided, the source said.
Chacon said she was overwhelmed by news of the shooting and spent the past several days crying inside her home.
"I want this to stop," she said.
After speaking to reporters for about 10 minutes, Chacon turned and walked back inside her stucco Riverside home.
She was still crying.
Parvin, Mather and Queally reported from Los Angeles and Serrano from Washington. Staff writer Richard Winton in Los Angeles contributed to this report.