The man accused of killing an El Cajon dentist and injuring two others pleaded not guilty during his arraignment Tuesday. Mohammed Abdulkareem, 29, is charged with one count of murder and two counts of pre-meditated attempted murder charges related to the February 29 shooting at Smile Plus Dentistry in El Cajon. "The defendant was known to the dentist office. He had been a prior patient. He had consistently over months been dissatisfied and gone in repeatedly to that dentist office, such that his behavior was erratic and they were afraid of him," said Prosecutor John Philpott. MORE: https://www.cbs8.com/article/news/local/man-accused-of-killing-el-cajon-dentist-in-court/509-e398ce40-d0da-4437-9b7c-91440e9af9d7