A Nassau police officer testified Wednesday that a driver admitted having four vodka drinks before his arrest at a 2012 highway crash scene where a veteran cop suffered injuries that ended his life.

The testimony of Officer Matthew Davis in a Mineola courtroom kicked off a pretrial hearing for James Ryan, of Oakdale, now 28. Ryan has pleaded not guilty to charges that include aggravated vehicular homicide in the Oct. 18, 2012 death of Nassau police Officer Joseph Olivieri Jr.

Authorities have said a different motorist struck Olivieri with his Cadillac Escalade while the officer was crossing the Long Island Expressway on foot in North Hills.

Prosecutors say Ryan is responsible for Olivieri's death because the officer was responding to crashes caused by Ryan's alleged drunken driving.

Davis testified he heard Olivieri tell colleagues to step up their response rate after an early-morning call came in about an accident. He said he then heard an "officer down" notification, and arrived to see an officer standing over Olivieri at the scene.

"He was not moving," Davis testified, as Olivieri's father listened in the courtroom.

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Davis said Ryan told him his Toyota Camry had been hit several times, and an officer had been struck, too, but he didn't know how the accident happened. He testified he smelled alcohol on Ryan, heard him slurring words, and saw he had bloodshot eyes and bad balance. The officer said Ryan told him he'd had four vodka drinks and had been coming from a New York City nightclub.

"I believed he was intoxicated," Davis told Maureen McCormick, chief of the district attorney's Vehicular Crimes Bureau.

The officer said he arrested Ryan on charges of driving drunk and rode with him in an ambulance to a hospital before Ryan waived his Miranda rights and consented to a blood draw.

Nassau Det. John Lapine testified Wednesday that Ryan signed a statement at the hospital. It said he'd had three vodka drinks -- including one with two shots -- at a nightclub and was driving home when another vehicle hit his car, before he pulled over and was hit again.

Ryan's statement also said an officer came over and asked him if he was OK, before his car was hit "a third or fourth" time and he heard people yelling "Officer down, officer down."

In 2013, a Nassau judge dismissed the top charge and six other criminal counts, finding Olivieri's death "solely attributable" to the Cadillac driver's actions. But an appellate court reinstated the charges in February, finding there was "legally sufficient proof" before the grand jury that Ryan's actions "caused" the officer's death.

Prosecutors decided that the Cadillac driver's actions weren't criminal and he received immunity from prosecution by testifying to the grand jury.

Olivieri, 43, a father of two and Middle Island resident, had been a 13-year veteran of Nassau's police force after five years with NYPD.

The hearing continues Oct. 7, before a judge determines if certain evidence can be used at trial. That includes some alleged statements by Ryan that one of his defense lawyers, Marc Gann of Mineola, said Wednesday weren't disclosed in time. But prosecutors say they met all legal requirements.