Individual radicalization often comes through close friends and family members, rather than just external teaching and preaching. Sibling bonds are not the only family connections that have played a role in recent terrorist attacks.
(L-R) Tashfeen Malik and Syed Rizwan Farook, a married couple, died in a fierce gun battle with authorities several hours after their commando-style assault on a gathering of Farook's work colleagues at the county's health department in San Bernardino, California on Dec. 2, 2015.
Farook was a 28-year-old American citizen born in Chicago and employed with the San Bernardino County Department of Health. Farook traveled to Saudi Arabia for two weeks in July 2014 to pick up his fiancee, Malik, 27, who is Pakistani, a law enforcement source told CBS News. Malik received a K1 Visa, known as a fiance visa. It's unclear when the visa was issued.
A former coworker of Farook, Chaz Harrison, described him as "very passionate" about his religion, and said that both he and his wife did not want to be in the U.S. According to the FBI, the San Bernardino killers had been radicalized "for quite some time" and had taken target practice at area gun ranges, in one instance just days before the attack that left 14 people dead.