A suburban exterminator has been charged with strangling a young Philadelphia doctor found bound and burned in her downtown row home, police announced Thursday.

Jason Smith, 36, was arrested Wednesday night at his home in Levittown, about 25 miles northeast of the city, homicide unit Capt. James Clark said at a news conference.

Smith was charged with murder, arson, abuse of a corpse and risking a catastrophe in the slaying of Dr. Melissa Ketunuti, 35, on Monday afternoon. He had no prior criminal record other than "minor traffic offenses," Clark said.

"She needed an exterminator, she called a certain service, he was subcontracted out," Clark said. "They got into some type of argument. It went terribly wrong."

Smith "struck her while she was in the basement, knocked her down, strangled her to death and ultimately set her body on fire" in an apparent attempt to hide evidence, Clark said. There were no signs of sexual assault and nothing was stolen from the home of the victim, whose body was bound with rope at her wrists and ankles and wrapped around her neck, police said.

Investigators said Smith, who lived with his longtime girlfriend and her young child, and Ketunuti, a second-year infectious-diseases fellow and researcher at the renowned Children's Hospital of Philadelphia, had never met before. Clark would not elaborate on the substance of the fatal argument.

"It's very tragic," he said. "You have a young physician who dedicated her life to helping people and to die in this tragic manner, it's very, very sad."

Ketunuti, who had been having a problem with rodents in her house, was running errands around the neighborhood just before meeting up with the exterminator, Clark said.

He said detectives watched hours of surveillance video from nearby businesses, one of which shows Smith entering Ketunuti's home with a work bag and dressed in a coat and gloves, then leaving without a coat less than an hour later. Other video shows the suspect getting into his truck after the slaying and driving past her home several times, Clark said.

"Detectives did an unbelievable job of finding every bit of footage that was in that area," Clark said.

Smith was in custody and unreachable for comment. It could not be immediately determined if he had an attorney.

District Attorney Seth Williams commended homicide detectives who worked tirelessly to quickly solve the case and he expressed his condolences to those who knew the victim.

"I would first like to send my thoughts and prayers to the family, friends and neighbors of Melissa Ketunuti," he said. "I know their pain must be enormous and I hope that today's arrest will help ease some of that pain."

Ketunuti's parents are in the process of making arrangements to travel from their home in Thailand to Philadelphia, Clark said.