A Suffolk County grand jury has upgraded charges against an off-duty police officer accused of driving while drunk and the wrong way on Sunrise Highway before hitting a van head-on and killing its driver, court records show.

Suffolk police Officer Robert Scheuerer, 24, was charged in an eight-count indictment Thursday with aggravated vehicular homicide, several lesser homicide charges, second-degree reckless endangerment and aggravated driving while intoxicated.

He faces a maximum of 9 1⁄3 years to 26 years in prison if convicted of all charges.

Scheuerer, assigned to the Third Precinct, has been suspended without pay. He will plead not guilty when he is arraigned on the indictment later this month in state Supreme Court in Central Islip, his attorney, William Petrillo of Rockville Centre, said Friday.

Petrillo said Scheuerer is out of the hospital but still recovering “from very serious injuries.” He declined to detail the injuries.

The Suffolk district attorney’s office declined to comment.

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Prosecutors have said Scheuerer had a blood-alcohol level of 0.17 percent — more than twice the legal threshold of 0.08 percent — on Sept. 27 when he crashed his 2000 Nissan Pathfinder into a 2016 Ford van. The van caught fire, killing its driver, Brian J. Fusaro, 37, of Bay Shore.

A law enforcement source said Friday the 0.17 percent blood-alcohol result came from a blood sample drawn three hours after the crash. An estimation technique known as retrograde extrapolation allowed prosecutors to conclude that Scheuerer’s blood-alcohol level was over the 0.18 percent necessary to prove aggravated vehicular homicide, the source said.

Some defense attorneys have cautioned that retrograde extrapolation has limitations. For example, if someone drank shortly before a crash, that person’s blood-alcohol content could rise for a brief time after the crash, before the alcohol begins dissipating in the body. If that was the circumstance in this case, Scheuerer’s blood-alcohol level could have been below 0.18 percent at the time of the crash.

It is another potential complication in a case that has exacerbated tension between police and the district attorney’s office. Although neither agency would discuss that tension publicly, several officials from both agencies have expressed dissatisfaction with how the other agency has behaved.

Police Commissioner Timothy Sini said he was unaware of the indictment Friday morning, but he praised police for their work on the case.

“The investigators handled this case entirely appropriately,” he said.

Scheuerer, who has been on the force for a year, had been drinking at a bar before driving the wrong way on the highway, prosecutors have said. The officer forced other motorists to swerve out of his way before the fatal crash in West Islip, prosecutors have said.

According to a transcript of Scheuerer’s arraignment at Southside Hospital in Bay Shore — which acting Suffolk County Court Judge David Morris barred the news media from attending — several motorists “flashed their lights” to get Scheuerer’s attention as he traveled east on westbound Sunrise Highway before the 4:37 a.m. crash in rainy weather, Assistant District Attorney Marc Lindemann said.

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“One tractor trailer had to slam on his brakes and swerve out of the way of the oncoming vehicle,” Lindemann said during the arraignment. “Another motorist had to pull over onto the shoulder to avoid a crash.”

Scheuerer is the son of Suffolk County police Sgt. Peter Scheuerer, a 27-year veteran of the force, sources have said.