Why did husband and wife kill 14?

While police say they know who massacred 14 people Wednesday at a holiday party in San Bernardino, California, the killers motives remain a mystery. Syed Rizwan Farook and Tashfeen Malik committed the deadliest U.S. mass shooting since Sandy Hook in December 2012 before being killed by police, authorities say. Here is what we know about them: Husband and wife Farook, 28, and Malik, 27,...