A Los Angeles doctor was arrested on Friday of second-degree murder in the deaths of three patients who overdosed on painkillers she prescribed. The prosecution of Dr. Hsiu-Ying "Lisa" Tseng was a rare murder case against a physician at a time when prescription drug abuse has become an epidemic and lawmakers have tried to make it harder for so-called pill mills to easily dole out medications with little scrutiny. A dozen of Tseng's patients died, including one who overdosed in her office. Prosecutors only brought three murder charges because of other factors involved in some of those deaths, such as drugs prescribed by other doctors and a possible suicide.