An NYPD officer pleaded not guilty to charges of second-degree murder and first-degree manslaughter Tuesday in an alleged road-rage altercation that left a man dead in July.

Prosecutors accuse Officer Wayne Isaacs of shooting Delrawn Small three times after leaving work in the early morning on July 4. Isaacs was off duty at the time.

Prosecutors say Small was unarmed and Isaacs shot him without legal justification.

"My office takes the prosecution of this matter very seriously and intends to prove the alleged charges against Mr. Isaacs beyond a reasonable doubt," says Attorney General Eric Schneiderman. 

The charges against Isaacs marks the first indictment since Gov. Andrew Cuomo's mandate requiring the attorney general's office to investigate all cases involving unarmed civilians killed by police officers. 

The defense described Isaacs as a married father of two who felt threatened when Small approached his car. Isaacs claims he shot Small out of self-defense when Small lunged at him through his driver-side window.