Pennsylvania's state police agency, facing pushback over its practice of investigating line-of-duty shootings by its own troopers, is trying to shut down a grand jury looking into the propriety of the policy.

Northampton County District Attorney John Morganelli

State police lawyers will be in court this week to argue the grand jury has no right to exist, let alone weigh in on whether Pennsylvania State Police should use outside law enforcement to probe shootings by troopers. Experts say police shooting investigations should be independent to ensure objectivity and avoid the perception of bias.

By seeking to silence the grand jury, the agency has invited criticism that it's trying to avoid scrutiny at a time of heightened national concern over fatal police shootings, said David A. Harris, a University of Pittsburgh law professor and expert on police practice.

"That shows a tin ear, at best, given the current climate," he said. "It shows a kind of 'trust us' mentality, and it just doesn't sit right in an era when more and more police agencies are moving toward more transparency and more accountability, not less."

State police declined comment on the grand jury because it is a pending legal matter.

The state police force, one of the nation's largest with about 4,200 troopers, is tangling with a county prosecutor who says it's inappropriate for law enforcement to review officer-involved shootings internally.

District Attorney John Morganelli sought the grand jury after state police, citing longtime policy, refused to allow his detectives to take the lead on a probe of a fatal trooper shooting near Easton. Troopers shot and killed Anthony Ardo on May 20 after he ignored their commands and attempted to light the fuse of a firework mortar around his neck.

The grand jury concluded last month that Ardo's shooting was justified. At Morganelli's behest, the panel has also been taking a look at state police procedure on investigating trooper-involved shootings and plans to issue a follow-up report. State Police Commissioner Tyree Blocker testified before the grand jury last month.

Agency lawyers have asked a judge to either shut down the grand jury before it's finished with the review, or prevent the public release of the report.

State police argued the grand jury is limited to investigating crime in Northampton County and has no legal authority to review its policies. Once the panel concluded that troopers were justified in killing Ardo, it was "case closed," lawyers wrote.

The judge plans to hold a hearing on the matter this week but said it will be conducted behind closed doors. Morganelli has petitioned the judge to open it because the dispute involves "an agency of state government attempting to shut down a grand jury investigation." Moreover, he said, police shootings and how they're investigated are issues of "high national interest and importance."

Morganelli declined comment beyond his court filing. A spokesman for the troopers' union also declined comment.

State police defended its procedure for investigating shootings by troopers.

"Pennsylvania State Police is confident in the protocols it has in place to ensure each trooper-involved shooting is investigated thoroughly and transparently," said police spokesman Ryan Tarkowski.

The agency noted that investigators from different barracks are assigned to use-of-force cases and work in consultation with prosecutors, who have the ultimate say over whether a shooting was justified.

But the state police policy runs counter to what's considered best practice.

The Pennsylvania District Attorneys Association recommended last year that investigations of police shootings be handled independently to avoid the perception of bias. A Wisconsin law, meanwhile, mandates that fatal shootings by on-duty police officers are investigated by outside law enforcement agencies.

Philip Stinson, a criminal justice professor at Bowling Green State University in Ohio, accused Pennsylvania State Police of "arrogance" in its insistence on running its own trooper-shooting investigations.

He also faulted state police for moving to quash the grand jury.

"I think it's completely inappropriate," he said. "If nothing else, there's nothing wrong with having the discussion. That's in the interest of the commonwealth."