EASTON, Pa. — A grand jury is investigating whether it’s appropriate for state police to investigate shootings by its own troopers, a prosecutor said Wednesday.

The panel has been hearing testimony on the long-standing state policy and should be ready to issue a report in a few weeks, Northampton County District Attorney John Morganelli said at a news conference.

Morganelli has been sharply critical of state police for refusing to relinquish its probe of the fatal shooting of a suicidal man, saying police departments should step aside when a shooting involves one of their own.

Guidelines issued by the Pennsylvania District Attorneys Association last year say that police shootings should be investigated by an independent agency.

“Evidence can be planted at a crime scene,” Morganelli said Wednesday, speaking generally. “I think that we’re always looking at trying to make sure that there’s public confidence in an investigation, and the best way to do that is to clear the decks and have the agency move out of the way.”

State police defended the policy, saying it has “strict guidelines and protocols” to ensure thorough investigations of shootings by its own troopers. The agency noted that investigators from different barracks are assigned to those cases and work in consultation with prosecutors.

“We feel strongly that the department has the resources in place to conduct unbiased, independent investigations at all times,” said Cpl. Adam Reed, a state police spokesman.

The grand jury report will not carry force, but Morganelli said it could spur change, either administratively or through legislation.

The prosecutor had convened the same grand jury to conduct an independent probe of the May 20 shooting of Anthony Ardo after state police, citing policy, had refused to yield the probe to his detectives.

The grand jury, which viewed police dashboard camera video of the shooting, voted unanimously to clear troopers Eddie Pagan and Jay Splain of any wrongdoing. The troopers had responded to Ardo’s mother’s house after she reported that her volatile, aggressive son, against whom she had obtained a protection-from-abuse order, had showed up and was threatening suicide.

Ardo ignored their commands and attempted to light the fuse of a firework mortar around his neck while he was sitting in his car, the grand jury said. In testimony before the panel, Pagan “described a maniacal look and smile on Mr. Ardo’s face as he turned to look at Trooper Pagan while attempting to ignite the fuse,” the grand jury said.

The panel said the troopers were justified in shooting him. Had the mortar detonated, it could have pierced the car’s gas tank and caused an explosion that would have killed the officers, the grand jury said.