The Zajkos were found dead in their Chester Heights home on Jan. 2 by troopers conducting a welfare check, Daily Voice has reported.
Nearly a month later, police detectives say they have conducted "dozens" of interviews, executed "numerous" search warrants, and "obtained new evidence" in the course of the investigation.
"Based off this information it is believed at this time not to be a random act of violence," said Trooper Shyeasha Ayala in a statement.
The deaths of Richard, 72, and Rita, 69, have both been ruled homicides, though authorities have not said how they died.
According to the Philadelphia Inquirer, police were called by a family member on Jan. 2 who had not heard from the couple in a long time, and asked them to conduct a welfare check. It's not clear when investigators believe the pair were murdered.
Neighbors told the newspaper the couple had lived in their Highland Drive home for decades.
Anyone with information is urged to contact the Pennsylvania State Police's Troop K at Media Station by calling 484-840-1000. To submit an anonymous tip, call 1-800-472-8477.
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