The Goa police have found empty bottles of a cough syrup in a room where the CEO of a start-up allegedly killed her four-year-old son, indicating she might have given a heavy dose of the medicine to him and that it was pre-planned murder, an official said today. The postmortem has revealed the child was smothered to death either with a cloth or a pillow, as per officials. The accused woman, Suchana Seth, allegedly killed her son in the apartment at Candolim in Goa and stuffed the body in a bag before taking it to neighbouring Karnataka in a taxi, police said.