District Attorney Seth Williams said his office had not decided whether it would appeal. He said he was disappointed in what he called the judge's "acceptance of slanted factual allegations" and "a newly concocted alibi defense" that he contended was a lie.
The ruling marked a stunning turn in the 20-year legal battle over Dennis, whose cause drew supporters worldwide even as he lost appeal after appeal.
One of his lawyers, Ryan Guilds, said Dennis, 42, broke down when he received the news in a phone call Wednesday at the state prison in Waynesburg, in the southwestern corner of Pennsylvania, where he has been on death row for two decades.
"We are believers of God, so we always believed that the truth would eventually come out," his brother, Tony, said in an interview.
His mother, Juanita, and sister, Hope, were joined at their Germantown home Wednesday night by James Dennis' daughter, Kiara Everett, who was born shortly after his arrest, and his godmother, Maxine Brockington.
"We've been praying for this day for 21 years," Juanita Dennis said. When she got the news from her son's lawyer, she said, "I was on my feet. I was dancing."
Hope Dennis said her brother spoke with his family on the phone Wednesday night. "He said, 'God is moving right now,' " she recalled.
Everett has a 4-month-old daughter, Zanylah, whom Dennis has yet to see in person. He has not seen any family members in five years. He stayed in touch by phone, but personal visits had become too painful for him, his sister said.
While advances in evidence collection and DNA analysis have led to hundreds of exonerations, Brody's ruling reflected a newer wave in wrongful-death appeals. It involved no groundbreaking developments, confession, or irrefutable proof of another killer.
Instead, a team of appellate lawyers spent years reinterviewing witnesses, chasing evidence, and ultimately persuading a judge that the investigation and prosecution were too suspect or flimsy from the start.
The October 1991 killing of Chedell Ray Williams, a 17-year-old Olney High School student, for a $450 pair of earrings outraged city officials and put a spotlight on what had been a surge in violence over jewelry.
Eyewitnesses said two assailants approached the girl as she walked up the station steps and demanded her earrings. One shot her, and they fled in a waiting car.
Dennis, then a 21-year-old aspiring singer from West Oak Lane, was the only suspect arrested or charged. He contended he had been riding a SEPTA bus from his father's home at the time of the killing, an alibi later corroborated by another bus rider.
Police never recovered a weapon or the earrings, and developed no forensic evidence tying Dennis to the scene. He was convicted largely on the testimony of three eyewitnesses. The jury deliberated about 90 minutes before agreeing on the death penalty.
Brody's opinion cited a slew of reasons the case troubled her - from shoddy police work to lost evidence and a trial lawyer, Lee Mandell, who the judge said did only "the bare minimum" to defend Dennis.
She called the eyewitness identifications "shaky" and noted that half of the people who claimed to have seen the shooter described a taller and heavier man. Police targeted Dennis based solely on "neighborhood rumors," the judge said.
His only previous conviction was for drug possession, but he was later convicted in an earlier unrelated shooting. Dennis has denied that crime as well.
In the end, Brody hinged her ruling on a key tenet of the trial system. She said prosecutors and investigators had withheld evidence that could have bolstered Dennis' innocence claims and given jurors reasonable doubt.
According to the judge, police blatantly ignored other leads and failed to share them with the defense, tactics she called "underhanded and illegal." One was a sworn statement from a Montgomery County inmate three weeks before Dennis' arrest in which the inmate said his cousin had admitted the fatal robbery. Lawyers for the District Attorney's Office later dismissed that tip as "a fruitless" lead.
"The primary reason it was fruitless was because detectives simply ceased to investigate the matter," the judge wrote.
Dennis also was never told that police knew that Zahra Howard, a teen who was walking with Williams that day, had told relatives she recognized the assailants from her high school, and even mentioned their nicknames.
Finally, Brody highlighted what she said was flawed trial testimony from an acquaintance of Dennis' who could have been his strongest witness.
LaTanya Cason testified that on the day of the slaying, she picked up her welfare check around 3 p.m., ran errands, and saw Dennis between 4 and 4:30 p.m. on a bus near the Abbotsford Homes on McMichael Street, nearly five miles from the crime scene.
Years after the trial, appeals lawyers found a Welfare Department receipt showing Cason actually got her check closer to 1 p.m. and thus would have seen him on the bus closer to 2:30 - around the time police said the killing took place. Cason later gave a sworn statement on Dennis' behalf acknowledging that she probably saw him on the bus earlier than she had testified.
The prosecution once acknowledged that it had lost Cason's receipt, but a state appellate court ultimately said that had no real bearing on Dennis' alibi. Brody disagreed, concluding that sharing it with the defense might have provided "strong evidence that he was nowhere near the crime when it occurred."
According to the judge, some of the mistakes could have been caught or corrected at the time if Dennis had had a vigorous lawyer. She said Mandell failed to interview a single eyewitness, test the evidence, or enlist experts.
Mandell did not return a call seeking comment Wednesday. The assistant district attorney who prosecuted the case, Roger King, retired in 2008 and could not be reached for comment Wednesday.
Tracy Lamourie, an activist in Toronto, said she and her husband, Dave Parkinson, first came across Dennis' name on a prisoner pen-pal petition in 1998, and became fascinated by his case. Their Justice for Jimmy Dennis campaign now has representatives in 15 countries, she said, and all were elated by the news.
Two years after that, a team of lawyers from the Washington firm of Arnold, Porter took on the case free, working with federal public defenders in Philadelphia.
In March 2011, Gov. Corbett signed a death warrant for Dennis. Another federal judge stayed the execution, and the case landed with Brody.
Contact John P. Martin at 215-925-2649, at email@example.com or @JPMartinInky on Twitter.
Inquirer staff writer Robert Moran contributed to this article.