On September 4, 2006, Kathy Wangler, wife of anesthesiologist Dr. Mark Wangler, died from carbon monoxide poisoning in their home in Lima, Ohio. Their thirty-year marriage had been falling apart; three years later, in 2009, investigators came to the conclusion that Dr. Wangler had murdered his wife. Kathy’s mother and sisters felt that since Mark was familiar with gasses that he was able to plan and execute the perfect murder. Mark was arrested and the case was brought to trial. “48 Hours" correspondent Peter Van Sant reports. This classic "48 Hours" episode last aired on 6/16/2012. Watch all-new episodes of “48 Hours” on Saturdays, and stream on demand on Paramount+. See Privacy Policy at https://art19.com/privacy and California Privacy Notice at https://art19.com/privacy#do-not-sell-my-info.