Man charged in Philly doctor's death

NEW: Doctor's alleged killer came to her house to deal with rodent problem, police say NEW: Jason Smith is charged with murder, other counts in Melissa Ketunuti's death NEW: Other than traffic offenses, Smith has no criminal record, police say Ketunuti's dog walker found her bound, burned body in the basement of her home

Philadelphia (CNN) -- The unsettling case of a doctor killed and set on fire in her Philadelphia home took another turn Thursday as police identified her alleged killer as an exterminator sent to her home to help clear it of rodents.

Jason Smith, 36, of Levittown, Pennsylvania, was charged Thursday with murder and other counts after detectives, using surveillance video and tips, identified him as the alleged killer of Melissa Ketunuti, a well-liked doctor and researcher at Children's Hospital of Philadelphia.

Police say Smith got into an argument with Ketunuti in the basement of her row home in an affluent area of downtown Philadelphia. He knocked her down, then strangled her and then set her body on fire, police Capt. James Clark said at a news conference.

He declined to elaborate on the argument but said Ketunuti and Smith had never met.

"We're glad for the family we're at least able to give some closure with the arrest of this individual," Clark said.

Surveillance video shows Smith approaching her home and going inside at Ketunuti's invitation, he said.

"She was expecting him. They had an appointment," Clark said.

Once inside, an argument erupted that quickly escalated into a physical altercation.

Smith struck Ketunuti, knocked her to the ground and strangled her with a rope he found in the basement, Clark said. Eventually, he set her body on fire, he said.

Ketunuti's dog-walker discovered the body, according to police.

Smith lives in Levittown with his girlfriend and her young daughter, Clark said. Other than minor traffic offenses, he has no criminal record, he said.

He is charged with murder, possession of an instrument in a crime, abuse of a corpse and causing catastrophe, according to Tasha Jamerson, a spokeswoman for the Philadelphia district attorney's office.

It was not immediately clear when he was to appear in court.

Levittown is about 30 miles away from Ketunuti's home.

Ketunuti, who graduated from medical school in 2007, moved to Philadelphia from Washington in 2008 for a three-year residency in pediatrics. She was in her second year of working as a researcher and fellow in infectious diseases, the hospital said.

She previously had residencies in surgery at Georgetown University Hospital in Washington and cardiothoracic surgery at a veterans hospital.