A dentist was shot and killed at his California office Thursday by a “disgruntled” former patient who planned out the slaying weeks in advance, according to police. Mohammed Abdulkareem, 29, allegedly stormed into Smile Plus Dentistry & Orthodontics wearing all-black clothing around 4:15 p.m. and opened fire, striking two adult men and one adult woman. The gunman then hopped in a U-Haul pick-up with Arizona plates and fled the scene, the El Cajon Police Department said. 3 Mohammed Abdulkareem allegedly shot three people, killing one, at a California dental office. El Cajon Police Department First responders arrived within just two...