Complex sentence: Syed Rizwan Farook and Tashfeen Malik had left their six-month-old daughter with Farook's mother on the morning before the attacks, telling her that it was because of a doctor's appointment.
Split into simpler sentences: Syed Rizwan Farook and Tashfeen Malik had left their six-month-old daughter with Farook's mother the morning before the attacks. They told her that it was because of a doctor's appointment.