An eighth-floor Philadelphia courtroom turned into a time machine Tuesday, reaching back to the early hours of Aug. 24, 1985, when, prosecutors say, Daniel Dougherty killed his two young sons by setting fire to the family home.

Old black-and-white photos of the burned Oxford Circle rowhouse were shown on a screen. The boys' babysitter that night - then 9, now a grown woman - testified how she put the children to bed. A now-retired police officer told the jury how he arrived at a horror scene, knowing that children were inside the house and seeing flames "coming out like a blast furnace."

"That's something you don't forget," former Sgt. William Rhoads testified.

Seventeen years ago, Dougherty was tried, convicted, and sentenced to death for the murder of 4-year-old Daniel Jr. and 3-year-old John at their Carver Street house.

Dougherty, 56, has always insisted that he is innocent, that he awoke to a house ablaze, ran outside, then tried desperately to rescue his boys. Nearly 31 years later, he's counting on advances in fire science to prove he committed no crime.

The case holds national implications, a prime example of evolving fire science that has freed some inmates and brought the guilt of others into question. Scientists now dismiss many of what once were considered classic signs of arson, fueling a debate over how the justice system should handle convictions based on now-discarded beliefs.

Dougherty in 2014 was granted a new trial after an appellate court found that his lawyer's failures so skewed the original proceeding that "no reliable adjudication of guilt or innocence took place."

In opening arguments Tuesday, Assistant District Attorney Jude Conroy said evidence would show Dougherty was guilty not beyond a reasonable doubt, but beyond all doubt.

He said a drunk and angry Dougherty ended up alone in the home, his two sons upstairs, after battling both his girlfriend, Kathleen Schuler, with whom he lived, and the boys' mother, Kathleen Dippel, from whom he was separated.

"An open flame," Conroy said, describing the fire's source. "To the couch, to the love seat, to items under the table."

Conroy said he would present the earlier testimony of John Quinn, who at the time of the blaze was an assistant city fire marshal. Quinn, Conroy said, got it right when he ruled the fire an arson, based on burn patterns that showed the fire started in three places.

But if Quinn and police were certain of Dougherty's guilt, defense lawyer David Fryman asked, why didn't they arrest him that day? Or a month later? The evidence against him was known, he said. But he wasn't arrested until 14 years later, in 1999.

Fryman called the original inquiry "flawed," saying investigators failed even to take a standard photo of the stove, to show whether the knobs were in an on or off position.

"The commonwealth claim that this fire was intentionally set doesn't have any validity," he said.

Fryman did not tell the jury the circumstances around Dougherty's arrest. The Inquirer reported at the time that Dougherty was charged after his estranged second wife, Adrienne Sussman, then battling him for custody of their son, Stephen, called police and told them he had confessed to her.

She never testified at his original trial. She has died. Dougherty's original lawyer, Thomas Ciccone, has died, too. So have other potential witnesses.

Former officer Rhoads testified that upon reaching the scene, he helped another officer handcuff a crazed, near-hysterical Dougherty outside the burning home.

His memory isn't as good now as it was 32 years ago, Rhoads said, but he distinctly recalls how Dougherty answered when asked for his name:

"My name is mud and I should die for what I did."

Rhoads, believing that was an admission of guilt, had Dougherty transported to the homicide division, but he was not charged.

That single sentence was the only thing Dougherty said, Rhoads testified under defense questioning Tuesday.

"You didn't hear him crying for someone to save his children?" counsel Shannon Farmer asked.

"No," Rhoads answered.

"Your testimony is he was in a silent hysteria?"

It's unclear if the jury knows it's hearing a retrial. The attorneys have referred only to "an earlier proceeding."

Dougherty's death sentence was vacated in 2012, becoming a life sentence, after prosecutors agreed with the defense on the ineffectiveness of his trial lawyer.

215-854-4906 @JeffGammage