She urged the people of Lawncrest to step up with information in the case.
"I am begging this community that has experienced so many acts of tragedy and violence in recent months to come together and push back against this violence," Kunf said. "This neighborhood needs to regain some sense of peace, safety, and security."
Catherine Rohland, Donna Muller's sister, said mother and son were lifelong residents of Lawncrest. Both graduated from Cardinal Dougherty High School.
Philadelphia Homicide Capt. James Clark said the Mullers were each shot once in the head with a 9mm handgun. He called on the public for "information on this cold-blooded killer."
Clark said the slayings were not related to a triple homicide in February at a home in the 6300 block of Martins Mill Road in Lawncrest, in which the victims were shot in the head. Investigators have said they believe those slayings were drug-related.
Relatives said Donna Muller was an editor for a technology firm in Horsham, and Richard Muller, who worked part-time as a cook at a nursing home, was set to graduate in May with an associate's degree in information systems and technology from Manor College.
"We do not know why someone chose to murder them," Rohland said. "What is certain is that Donna and Richard Muller should not be dead. They were not violent people."
"Our family is living a nightmare," she said. "We are crippled by an endless grief that has destroyed all our lives."
The city is offering a $20,000 reward per victim for information leading to the arrest and conviction of the killer or killers. To leave a tip, call 215-686-TIPS (686-8477).