A month before the murder trial of former Philadelphia Police Officer Ryan Pownall for fatally shooting a North Philadelphia man during a traffic stop, prosecutors are taking aim at the state law that allows police to use deadly force in some circumstances.

The District Attorney’s Office has asked the judge to give jurors instructions about the state’s use-of-force law that would essentially undercut what is expected to be the main theory of Pownall’s defense: That he was legally justified in firing his gun at David Jones, who ran away from Pownall after being stopped while riding a dirt bike and illegally carrying a firearm in 2017.

The reason, Assistant District Attorney Tracy Tripp said in a motion last week, is that her office believes the current state law — which says in part that police can use deadly force if someone commits a felony and is attempting to escape arrest — not only violates the Pennsylvania Constitution, but also undercuts Fourth Amendment protection against unreasonable search and seizure.

Pownall’s attorneys on Wednesday filed a blistering response, calling the maneuver “truly unimaginable” and an attempt by District Attorney Larry Krasner’s office to change a law weeks before trial in order to make its case easier to win.

“This may be the first time in Pennsylvania’s history that an elected district attorney intentionally ignored the law in bringing charges against a peace officer, and then sought judicial intervention in changing the law before a trial on those unlawfully brought charges,” said the motion signed by Fortunato Perri Jr.

Perri declined to comment further. Tripp said prosecutors were not asking Common Pleas Court Judge Barbara A. McDermott to declare the law unconstitutional, but rather “to interpret the statute in a constitutional manner” in instructing jurors.

The filing was the latest unusual volley in the high-profile case. Last month, McDermott declined Perri’s motion to have Pownall’s trial on third-degree murder charges — scheduled to begin in January — heard before jurors from another county because of local publicity.

It was not immediately clear whether the recent motions would delay Pownall’s trial. Tripp said that was “certainly not our intention by any means.”

At issue is the statute governing when officers may use deadly force.

Krasner’s office said it had no issue with the statute’s first provision, which allows an officer to use deadly force "to prevent death or serious bodily injury” to the officer or someone else.

But prosecutors took issue with other aspects of the law that allow police to use deadly force to prevent a suspect from evading arrest, and when the suspect “has committed or attempted a forcible felony or is attempting to escape and possesses a deadly weapon, or otherwise indicates that he will endanger human life or inflict serious bodily injury unless arrested without delay.”

Tripp wrote that the law’s wording “essentially provides three scenarios where an officer may use deadly force even if he does not believe such force is necessary to prevent death or serious bodily injury.”

Perri, in addition to calling the district attorney’s motion a “thinly veiled attempt to bolster its weak case,” said changing the law “on the eve of trial” would violate Pownall’s constitutional rights if any new standard was retroactively applied.

On that point, Jules Epstein, a Temple University law professor, agreed, saying that changing criminal standards and then applying them to a defendant’s past conduct could raise "fundamental due process issues.”

Other aspects of Krasner’s strategy left legal experts divided.

Seth W. Stoughton, an associate law professor at the University of South Carolina who has written extensively about police use-of-force, said that states are not required to have laws ensuring that unconstitutional actions are criminally prosecuted.

He said that about half of the 50 states have police use-of-force laws resembling Pennsylvania’s, while some, including California and Washington, have recently toughened their standards for when police can use deadly force.

Krasner has been outspoken about changing how and when police are charged with misconduct. During his first week in office, he faulted his predecessors for not charging an officer for an on-duty shooting since the 1990s.

Bruce Ledewitz, a law professor at Duquesne University, agreed that states are not required to ensure that laws provide criminal penalties for constitutional violations. A victim, relatives, or even the state can sue in civil court over violations of the Fourth Amendment, Ledewitz said, but “if the state decides you can’t prosecute a police officer for committing an unconstitutional act, the prosecution is stuck with that."

David Rudovsky, a civil rights attorney and University of Pennsylvania law professor, said he was not persuaded by that argument. “To the extent that the state creates a defense that’s unconstitutional, I think there’s at least a plausible argument that that’s not permissible,” he said.

Still, Rudovsky was dubious about whether a new law should be applied retroactively to a criminal defendant “for conduct that the legislature appears to have authorized.”

Pownall was fired over the shooting in 2017. Then-Commissioner Richard Ross said Pownall had violated a host of departmental violations, including displaying “poor judgment,” for firing at Jones after Jones had dropped his gun and run away.