Philadelphia Doctor Slaying: Alleged Killer Jason Smith Had Anger Issues, Family Friend Says Jason Smith was a problem child as an adolescent, a family friend told ABC News.

Jan. 25, 2013  -- Jason Smith, the Philadelphia exterminator who police say showed up at the home of Dr. Melissa Ketunuti this week to solve her rodent problem before strangling her, was a problem child as an adolescent, a family friend told ABC News.

The family friend from many years ago, who asked for anonymity, said Smith, 36, had behavior and anger issues, and that he also liked to set things on fire.

After Smith and Ketunuti got into "some kind of argument" in Ketunuti's basement, he struck her, strangled her and set her on fire, according to police.

Smith reportedly admitted to the brutal slaying after hours of police questioning Wednesday night. Smith told police that Ketunuti had "belittled" him, sources told ABC News affiliate WPVI-TV in Philadelphia

He snapped and apparently tried to hide any evidence by setting the 35-year-old doctor on fire with paper he lit in the kitchen, the station reported.

"People like Mr. Smith basically walk around with a huge chip on their shoulder, and they feel so inadequate and so insecure that any perceived belittlement of them will set them off," ABC News consultant and former FBI agent Brad Garrett said.

Capt. James Clark of the Philadelphia Police Department said Smith's mood and clarity varied during his alleged confession.

"At some points, he was solemn. At other points, it was like he was in a fog," Clark said at a news conference.

Smith has been charged with murder, arson, abuse of a corpse and risking a catastrophe.

Ori Feibush, who owns a coffee shop near Ketunuti's street, said he and police pored over hours of surveillance video until they saw Ketunuti walking home from doing errands, with Smith steps behind her.

"Forty-five minutes later, we see this same guy walking past, but [he] looks a little more disheveled and he's got gloves on," Feibush told ABC News.

Police say that after the slaying, Smith circled Ketunuti's block twice, before heading off to another job.

Ketunuti was a doctor at the Children's Hospital of Philadelphia and had lived alone in the Graduate Hospital neighborhood of the city for about three years. Her family released a statement saying they are "devastated by this senseless act of violence."

"Melissa's friends from childhood, college, residency and elsewhere remember her many kindnesses, even during long hours, as well as her zest for life: traveling, running and spending time with friends and family," the statement said. "Melissa was a source of joy to everyone in her life. Her passing has left an enormous gap in our lives."