Police were also tracing her movements Monday morning from electronic transactions, and collecting video surveillance from the several places she visited in Center City, including a Walgreen's around the corner.
A police source said she was doing work-related errands, and investigators had established that she was back at her home in the 1700 block of Naudain Street in the Graduate Hospital section, shortly before 11 a.m. The attack apparently happened between then and Noon, the source said.
"She was in several different locations in center city. We've already backtracked two or three of them. So far we don't see anyone following her, but I have detectives out there right now still looking at some other locations we know that she was possibly at and looking for video that would possibly show her killer," Clark said.
Her boyfriend, a doctor from New York, has come to Philadelphia to assist in the investigation and is not a suspect, Clark said.
There was no sexual assault, Clark said, and he would say whether it was a targeted or a random attack.
"We don't know if she walked in on individuals inside her property. We don't know if individuals forced her inside her property. We don't know if it's a known doer or an unknown doer," Clark said.
Firefighters discovered Ketunuti's burning body in the basement, her ankles and wrists bound behind her back.
There was no sign of forced entry at Ketunuti's rowhouse on a well-maintained street blocks from Rittenhouse Square.
She was discovered around 12:30 p.m. by her dog walker, police sources said, who showed up to walk Ketunuti's pit bull/Lab mix, Pooch, and found the door unlocked and the body smoldering facedown in the unfinished basement.
Ketunuti was a second-year infectious diseases fellow and researcher at CHOP, and had been at the hospital a total of five years.
"Melissa was a warm, caring, earnest, bright young woman with her whole future ahead of her," Dr. Paul Offit, chief of the Division of Infectious Diseases, said in an official CHOP release Tuesday.
"But more than that," he said, "she was admired, respected and loved by those with whom she worked here at CHOP. Her death will have a profound impact on those who worked with her and we will all miss her deeply."
Contact Mike Newall at 215-854-2759 or firstname.lastname@example.org, or follow on Twitter @MikeNewall.