If there is something in the makeup of Jason Smith that might have presaged the slaying to which police say he has confessed, nothing was immediately apparent Thursday.

Neighbors in the Crescent Lane section of Levittown, Bucks County - where the 36-year-old exterminator lived with his girlfriend, their young daughter, his girlfriend's mother, and other relatives - described him as helpful, a family man who took his boxer, Tyson, out for frequent walks.

They said he showed no signs of a violent temper.

Yet Philadelphia police officials, at a news conference Thursday, said an explosive argument between Smith and Melissa Ketunuti apparently triggered a murderous rage.

Police said Smith told them that the brutal assault occurred during an argument over his services with Ketunuti, 35, a pediatrician at Children's Hospital of Philadelphia. According to investigators, Smith said he knocked her to the floor, bound her hands and feet, and strangled her, and then set her head and chest on fire in an effort to destroy evidence.

A dog walker found Ketunuti's body in the basement of her Center City rowhouse on Monday.

Speaking on condition that they not be identified, police investigators said Smith's statement, in which he said he "just snapped," included an admission that he was addicted to prescription painkillers and had a history of drug and alcohol abuse.

On Thursday, Smith was charged with murder, abuse of a corpse, and risking arson. Investigators said Smith had no significant criminal history.

Court records show Bristol Township police arrested Smith on Feb. 18, 2004 - his 28th birthday - for allegedly driving under the influence of alcohol and cocaine.

When police encountered him, he was stopped at the scene of an accident on Route 413 just north of Bath Road. His car was severely damaged.

After pleading guilty to three counts of dangerous driving, he was sentenced to one to six months in county prison, ordered to enroll in a substance-abuse treatment program, and assessed $1,808 in court costs and fines.

He served one month in prison and was released, completed the court-ordered treatment program, and agreed to pay his fine at the rate of $50 every two weeks. At that time, he lived on Ritter Avenue in Bristol, and paid $75 a week in child support. Neighbors say he has two children.

On the day of the killing, Smith was working as a subcontractor for Dave Bilyk Exterminators, a Newtown company founded in 1992. A person who answered the phone at Bilyk on Thursday said, "No comment," and immediately hung up.

A man who answered the door at Smith's Crescent Lane house also declined to comment.

In addition to the Crescent Lane and Ritter Avenue addresses, public records show that for a time, Smith lived in Langhorne.