Last Updated Dec 3, 2015 3:06 PM EST
The FBI and police are searching the Redlands townhome tied to San Bernardino shooting suspect Syed Rizwan Farook. Late Wednesday night, police used a battering ram to enter the home and sent a robot in to sweep for possible explosives.
Police have identified Farook, a 28-year-old American citizen born in Chicago and employee with the San Bernardino County Department of Health, and Tashfeen Malik, a 27-year-old female who is Farook's wife, as the two suspects involved in the shooting.
Police said Farook was at a holiday banquet with coworkers before leaving abruptly and returning with his wife. Shortly after, shots were fired, reports CBS News' David Begnaud.
"I am in shock that something like this could happen," said Farook's brother-in-law, Farhan Khan.
Khan told CBS News that Farook and Malik were married for two years and had a 6-month-old child, who they left with Farook's mother.
Farook traveled to Saudi Arabia for two weeks in July 2014 to pick up his fiancee, Malik, who is Pakistani, a law enforcement source told CBS News. Malik received a K1 Visa, known as a fiance visa, a U.S. official told CBS News. It's unclear when the visa was issued.
A source told CBS News that the pair were looking at ISIS propaganda online.
At a press conference with local Muslim leaders, Khan offered his condolences to the families of the victims and expressed his disbelief.
"I have no idea why would he do that? Why would he do something like this. I have absolutely no idea," Khan said.
CBS News investigative producer Laura Strickler spoke online to a former classmate and co-worker of Farook. The former coworker, Chaz Harrison, was frantically trying to reach Syed and had no idea he was involved in the shooting when contacted by Strickler.
Harrison described Farook as "very passionate" about his religion, and said that both he and his wife did not want to be in the United States.
"I know he didn't want to be here, his wife didn't want to be here (USA). She was a pharmacist in her country," said Harrson.
Harrison said he had never met Farook's wife Malik, and that Farook was secretive about her.
"I did not attend his wedding. He was very secretive about his wife. I had to really ask him questions about her for him to tell me anything."
Harrison was shocked at the turn of events.
"Syed (Farook) was very passionate about his religion. He really felt some kind of way about the United States," said Harrison. "I never knew he would be this extreme."
Farook and Malik were killed in the police pursuit that ended in a shootout.
A federal law enforcement official tells CBS News both were dressed in tactical clothing, armed with assault rifles, and each had multiple magazines of ammunition attached to their clothing. Police also discovered handguns in their SUV.
The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) confirmed all four guns used in the attack were traced and purchased legally, reports CBS News' Justice Department reporter Paula Reid. Two of the guns were purchased by an unnamed person known to the investigation, officials said. The other two were purchased by an unknown individual.
Law enforcement officials do not have a motive yet, but say they are not ruling out terrorism. Police say they are confident the two suspects killed were the only shooters involved.