Last Updated Dec 6, 2015 5:30 PM EST
SAN BERNARDINO, Calif. - Early on Saturday, authorities with guns drawn raided a home next door to the house where family of one the shooters in the San Bernardino rampage used to live in Riverside, California, breaking windows and using a cutting torch to get into the garage, neighbors said.
The FBI would not say what it was looking for, but a neighbor said an old friend of Syed Farook's lives there.
CBS News senior investigative producer Pat Milton reports a law enforcement source says the target of the raid was Enrique Marquez, who is believed to have been the individual who three years ago bought the AR15 rifles in California used in the San Bernardino attack.
Marquez checked himself into a mental health facility after the attack.
The source told CBS News Marquez is not under arrest and is not considered a suspect in the shooting rampage. The source said that Marquez was employed as a security guard.
Another law enforcement source also tells CBS News they are confident only Farook and Marquez purchased the guns legally in California and reconfigured them to be more powerful. At this point they are confident no one else was involved in the purchase of the guns.
Law enforcement officials are also reviewing video from California gun store owners who have called saying they saw the two together.
Law enforcement is also taking their time with respect to Marquez, who is self-checked into a mental health facility, because he is the only credible eyewitness they have and they do not want to corrupt his potential testimony. The source says officials are not frustrated by not being able to interview him so far.
FBI agents seized numerous items during a search of Marquez's Riverside home early Saturday. The search warrant providing the probable cause to conduct the search as well as the items confiscated has been sealed.
In the final few years of Tashfeen Malik's life, the people around the young woman saw her dress ever more conservatively and urge people ever more ardently to live a devout life.
For an aunt in Malik's old hometown in Pakistan, Malik's growing religious focus was one of the last things she heard about her 29-year-old niece -- before last week, when she learned that her niece and her niece's husband had donned masks, hoisted assault rifles and killed 14 people in a rampage in Southern California.
"I recently heard it from relatives that she has become a religious person, and she often tells people to live according to the teachings of Islam," recalled aunt Hifza Batool.
Batool spoke in the town of Karor Lal Esan, the home of Malik's family, 280 miles southwest of the Pakistani capital of Islamabad.
Malik's path from Pakistan to the bloody events of last week -- when she and her husband slaughtered people gathered for a training session and holiday luncheon -- remains a mystery.
FBI officials, family lawyers and others said they know little about the housewife and mother, apart from what came to light on Friday: that Malik had pledged allegiance on Facebook to the Islamic State of Iraq ans Syria (ISIS) group as she and her American-born husband, Farook, 28, launched the massacre.
The husband and wife were killed in a furious shootout with police hours after they opened fire on a gathering of Farook's colleagues from the San Bernardino County public health department, where he worked as a restaurant inspector.
The FBI said it is investigating the rampage as a terrorist attack.
U.S. officials said Farook had been in contact with extremists via social media. One official said those contacts were not recent and did not involve any significant players on the FBI's radar.
Farook was born in Chicago to Pakistani parents and raised in Southern California. Malik arrived in the U.S. in 2014 on a Pakistani passport and a fiancee visa but had spent extended periods of time in Saudi Arabia.
She started studying pharmacy at Bahauddin Zakariya University in the Pakistani city of Multan in 2012.
Pakistani Interior Minister Chaudhry Nisar Ali Khan said Sunday that investigators so far have found no evidence linking Malik to Islamic militants.
He said his country is ready to share any information it has about Malik and her family.
"We have nothing to hide," he said.
A maid who worked in the Multan home where Malik lived said Malik initially wore a scarf that covered her head but not her face.
Former classmate Afsheen Butt said Malik showed drastic changes after a trip to Saudi Arabia in late 2008 or early 2009.
"She used to tell us that this is the real life. We are a nation that has strayed from the right path," Butt said. "She used to give us Islamic religious literature."
Saudi Interior Ministry spokesman Maj. Gen. Mansour Al-Turki said authorities there have received no indication Malik was radicalized in Saudi Arabia.
A year before she got married, she began wearing a scarf that covered all but her nose and eyes, the maid said. The maid spoke on condition of anonymity for fear of jeopardizing her employment with the family.
President Barack Obama planned to deliver a prime-time address to the nation Sunday night on the attack and the government's efforts to keep the country safe.