Doctor May Blame Double Murder on Cough Syrup Louis Chen accused of stabbing partner, 2-year-old son to death By Rob Quinn, Newser Staff Posted Dec 29, 2015 5:20 AM CST Updated Dec 29, 2015 7:29 AM CST 23 comments Comments Stock photo (Shutterstock) (Newser) – A doctor accused of murdering his partner and their 2-year-old son in 2011 will go on trial in April next year—and he may blame cough syrup for the grisly killings. Louis Chen's defense team in October filed papers signaling that they will argue that the 43-year-old was suffering from psychosis caused by a buildup of the drug dextromethorphan in his system, reports the Seattle Times. The defense declaration suggests Chen's Taiwanese genetic makeup made it harder for him to metabolize dextromethorphan, found in many over-the-counter cough medications. Police have suggested Chen killed partner Eric Cooper because of an impending breakup and custody battle in which Chen's alleged prescription drug abuse may have been exposed, the Times reports. When Chen didn't show up for his first day at work in a Seattle hospital in the summer of 2011, police found him covered in blood at his apartment, along with the bodies of Cooper and their son, Cooper Chen, the Seattle Post-Intelligencer reported at the time. Cooper had been stabbed more than 100 times and the toddler's throat had been cut. Chen, who fathered the boy with a surrogate mother, spent more than a week in the hospital being treated for self-inflicted stab wounds. University of Washington law professor Mary Fan tells the Times that she has "definitely heard of induced psychosis through taking various drugs," but not in any cases involving cough syrup, and she predicts the case will hinge on whether Chen's "intoxication" was voluntary or involuntary. Chen faces life without parole.