Montgomery County Coroner Walter Hofman ruled the death of Satyavathi Venna a homicide. Investigators responding to the apartment in King of Prussia on Monday discovered Venna's body and found the granddaughter, Saanvi Venna, missing. Authorities believe the abduction happened sometime between 8 a.m. and 1 p.m. that day.
Authorities on Thursday said they are increasing the award for information leading to the baby's safe return to $50,000.
The grandmother had been visiting from India since July, authorities said. She was scheduled to return home to India in January. No arrests have been announced in the case and police have released little information.
The coroner's office was at the scene Tuesday and Wednesday in investigating the woman's death, Hofman said. A message left for Montgomery County District Attorney Risa Vetri Ferman was not immediately returned Thursday.
Family members have issued pleas for the baby's safe return, and about 200 people attended a candlelight vigil Wednesday at a park in King of Prussia, about 15 miles west of Philadelphia.
Upper Merion Township police said the girl's father, Venkata Konda Siva Venna, and mother, Chenchu Latha Punuru, immigrated to the United States from India in February 2007.
Police issued an Amber alert for Saanvi on Monday following the discovery of her paternal grandmother's body at the apartment complex. That night, the girl's father made a tearful plea for his daughter's return.