Newsday says Anthony DiLeonardo escalated a roadside dispute with Thomas Moroughan before shooting him on Feb. 27, 2011.
The report says a doctor who treated DiLeonardo after the shooting noted he was slurring his words, smelled of alcohol and was hostile. Moroughan refused to provide a blood or urine sample.
DiLeonardo and his partner, Officer Edward Bienz, remain on duty.
The unit's findings were issued July 31, 2012. The report didn't say whether the officers should be criminally charged and whether departmental charges it recommended were ever brought.
Police officials and Bienz declined to comment. DiLeonardo didn't return calls seeking comment.