In the search for a suspect, detectives have reviewed security footage from several Center City locations Ketunuti visited before her death, Homicide Capt. James Clark said at a Tuesday news conference.
"So far we don't see anyone following her," Clark said, "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."
Task force members revisited the Graduate Hospital neighborhood Tuesday, collecting footage from the CVS store where Ketunuti shopped before returning home. They also retrieved footage from a nearby coffee shop and were reviewing footage from multiple cameras from the parking lot of Penn Medicine Rittenhouse, which overlooks 18th and Naudain Streets.
Coming from a meeting at the hospital and running errands in her car, police sources said, Ketunuti returned to the Naudain rowhouse she shared with her black pit-bull/Lab mix, Pooch, about 10:50 a.m.
She was killed between then and noon, police believe.
By 12:30, Ketunuti's dog walker had arrived to find the front door open and the doctor's body bound and burning in her basement, a rope pulled tight around the throat, police said.
The woman splashed water on Ketunuti and dialed 911. The burns covered Ketunuti's face and chest, police said.
"Her hands and feet had been bound behind her with some type of rope," Clark said. "There was some type of rope around her neck."
Though awaiting findings from the medical examiner, Clark said, "Right now it appears the cause of death was strangulation and then her body was set on fire."
The dog was in the house unhurt, and neighbors have said they do not remember the animal barking around the time of the killing.
Investigators still do not have a motive in the slaying of a doctor who dedicated her career to treating infectious diseases in young children. Police do not know if she was targeted by someone she knew or was followed home by a stranger.
"We don't know if she walked in on individuals inside her property," Clark said. "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."
Police sources said Monday that there were no signs of struggle in the home and that it remained unclear whether anything had been stolen.
Homicide investigators on Tuesday questioned Ketunuti's boyfriend, a surgeon at the New York University Langone Medical Center, who was in New York on Monday, Clark said, and not currently a suspect.
Investigators also visited Ketunuti's home Tuesday with the boyfriend, who was accompanied by two men at his side, in the hope he could help investigators determine what, if anything, might have been stolen.
Crime-scene investigators returned to the house while the boyfriend and detectives were inside, and left carrying several tagged bags of possible evidence.
Looking grief-stricken, the boyfriend did not respond to reporters' questions. "It's way too soon," one of the men accompanying him said.
Neighbors on the quiet, narrow street just blocks from Rittenhouse Square described Ketunuti as a polite and friendly woman who smiled in greeting when walking her dog, or taking a run, or often rushing with the demands of her work.
"She was super-pleasant, really nice," said Andrew Cattaneo, who said Ketunuti had few visitors to her home. "She had the dog walker that came every day and a housekeeper that came once or twice a week. That was about it."
A second-year infectious-diseases fellow and researcher at Children's, she had been at the hospital for five years.
After receiving her doctorate in medicine from Stanford University in 2007 - and working an AIDS research fellowship in Botswana - she worked a surgery internship at Georgetown University Hospital in Washington. She moved to Philadelphia in 2008 for a pediatrics residency program at Children's.
"Melissa was a warm, caring, earnest, bright young woman with her whole future ahead of her," Paul Offit, chief of the division of infectious diseases, said in a Children's 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.
Inquirer staff writer Alfred Lubrano contributed to this article.