Mr. Barclay himself even spoke of the role his own actions played in worsening his medical condition.

“The guy started spraying bullets around, and I caught two of them in the back,” Mr. Barclay said in a 1978 interview about the night he was shot. “I got over that pretty much, but then I had a car accident and hurt my back again. Then I had another and hurt my back some more.”

Allen M. Hornblum, an urban studies professor at Temple University who researched Mr. Barclay’s history and invited Mr. Barnes to speak to his class about having turned his life around after a career in crime, said the new charges were “vindictive, pure and simple.”

“Barnes served his time, but the police and the city want him to pay extra because he shot one of their own,” he said, adding that even if the charge is dismissed, the case will probably take so long to get to that stage that Mr. Barnes, who has had two heart attacks in the last three years, will die waiting. Ms. Abraham has denied that the victim’s being a police officer played any role in her decision to file new charges.

Ms. Abraham also argues that double jeopardy, which means a person cannot be charged twice for the same crime, does not apply in this case because the original crime was aggravated assault and the current crime — now that Mr. Barclay is dead — is murder. Mr. Barnes’s court-appointed lawyer has not decided whether to challenge that view.

William Barclay, 59, the slain officer’s brother, feels the prosecution is justified. “Barnes deserves to be back in prison,” he said “He is 71, and that’s seven more years of life than my brother had.”

Image William J. Barnes after his conviction in the shooting of Officer Barclay. Credit... Philadelphia Inquirer

“This was murder delayed,” Mr. Barclay added, recounting his brother’s bouts of pneumonia, painful and constant bedsores and the full-body muscle spasms that threw him from bed. “The length of time since the shooting shouldn’t matter.”