PITTSBURGH -- A federal prosecutor said her office and the FBI will start from scratch when they investigate the fatal state police shooting of a 12-year-old boy.

That means, among other things, that federal authorities won't rely on a Fayette County investigation that last month cleared two troopers of criminal wrongdoing -- and that additional witnesses might be interviewed in the latest probe of Michael Ellerbe's death, U.S. Attorney Mary Beth Buchanan said.

"We are encouraged that the FBI is going to take an independent look at the case, especially in light of what we've said all along -- that some witnesses were not being questioned," said Kelly Scanlon Graham, the law partner of attorney Joel Sansone. Sansone was hired to represent Ellerbe's family, which plans a lawsuit.

At a coroner's inquest last month, Trooper Samuel Nassan testified that he shot at Ellerbe after his partner, Trooper Juan Curry, fell over a fence while chasing the boy. Police said Ellerbe had run from a stolen vehicle he had been driving that afternoon in Uniontown, about 40 miles southeast of Pittsburgh.

When Curry's gun accidentally went off, Nassan said he believed his partner had been shot. Nassan fired, striking Ellerbe in the back and killing him.

Fayette County District Attorney Nancy Vernon, following the recommendation of a six-member coroner's jury, announced last month that no charges would be filed against the troopers.

Vernon said nothing in the 10 hours of testimony from a coroner's inquest and more than 50 interviews taken after the shooting discredited the troopers' version of events.

Buchanan said her decision to set aside Vernon's findings shouldn't be seen as a rejection of that investigation. But, Buchanan said, it is uncommon for federal officials to conduct an entirely separate investigation because resources are scarce.

"We couldn't possibly do this in each and every case," Buchanan said.

The National Association for the Advancement of Colored People had asked federal authorities to conduct a separate probe, but Buchanan said she wasn't bowing to political pressure.

Race has been an issue in the case because Ellerbe is black and Nassan is white. Curry, who also chased the boy with his weapon drawn, is black.

Buchanan said her office will contact Sansone and interview any witnesses the attorney believes might have been missed in the other investigation.

"If there are additional witnesses, we certainly want to speak with them," Buchanan said.

The Civil Rights division of the Justice Department will be consulted about whether charges are warranted once the federal investigation is finished, she said.

Nassan and Curry remain on administrative duty. State police officials have said they will not comment until their own internal investigation is complete.