A convicted killer who served time for murdering his friend in a Hicksville park 23 years ago is now heading back to prison.

Robert D'Andrea pleaded guilty Wednesday in Mineola to having a loaded, illegal handgun and heroin in his car when he was pulled over in Oceanside back in May.

He had been released on parole after serving 10 years behind bars for the shotgun murder of Bryan Levine, 16, who was found dead in Libby Park.

Nassau Homicide Detective Michael Kuhn picked up the cold case and arrested D'Andrea in 1999 for the 1993 murder. He says it took six years because, at first, none of the neighborhood teens would talk.

"As they got older and more mature, they realized how heinous of a crime this was," says Kuhn.

D'Andrea, who was 15 years old at the time of the murder, had been sentenced to seven years to life.

On the new charges, a judge promised him five years behind bars when he is sentenced in September.

D'Andrea's legal aid attorney declined comment about the case.