Authorities won't prosecute a Maryland State Police trooper who fatally shot a man at a Frederick gas station last fall after investigators said he rammed a city police cruiser with a stolen SUV and then lunged at the trooper, according to a letter the local prosecutor's office released Wednesday.

In the letter, dated Monday, Frederick County State's Attorney Charlie Smith told state police homicide unit Cpl. Anthony Dubas that Trooper 1st Class William Jansen used justifiable force in shooting Kevin Brunson, 45, of Baltimore on Oct. 25.

"Therefore, we are declining prosecution and consider this matter closed," Smith wrote.

The state's attorney's office refused to release investigative documents and video, deferring to state police, who investigated the shooting. State police spokeswoman Elena Russo said she couldn't release the materials because they are part of a continuing internal investigation.

State police said in October that Brunson was shot four times in the torso in the Sheetz parking lot. The agency said investigators found a folding knife with a 4-inch blade in Brunson's possession. It wasn't clear if Brunson was holding the knife when he was shot.

Brunson was suspected of having stolen the Lincoln Navigator a day earlier in Baltimore, state police said. They said Brunson had threatened the SUV's owner with a gun in his waistband. No gun was recovered at the gas-station shooting scene, police said.

Brunson's criminal history included convictions for robbery, theft and assault, and arrests for vehicle theft and carjacking, court records show. He was sentenced to three years in prison in 2013 for unauthorized removal of property.

Jansen is white, and Brunson was black. Race has not been raised as a factor in the shooting, but it came amid a national debate about the deaths of black men at the hands of police.