The prosecutor who took the rare step of charging a doctor with murder in the prescription drug overdose deaths of three patients said Friday that the case should serve as a warning to unethical physicians who become pill pushers. Los Angeles County District Attorney Steve Cooley said his office will continue to prosecute greedy and unethical doctors after charging Dr. Hsiu-Ying "Lisa" Tseng, 42, with second-degree murder and 21 other felony counts. If convicted of all the charges, she faces a maximum sentence of 45 years to life in prison. Authorities have been cracking down on drug deaths, which fueled by prescription drug overdoses now surpass traffic fatalities.