19-year-old Liam McAtasney is accused of killing Sarah Stern and dumping her body off a bridge in Belmar.
His friend Preston Taylor pleaded guilty to helping dump her body, and has agreed to testify against McAtasney.
Authorities say Stern was strangled during a robbery late last year.
Her remains have never been found.
Stern was last seen at her home on the night of December 2. Hours later, her unoccupied vehicle was found on the Route 35 Bridge in Belmar over the Shark River Inlet with the keys still in the ignition.
Monmouth County Assistant Prosecutor Meghan Doyle said the state will seek a life sentence without parole in the case against McAtasney, who also faces charges of robbery, conspiracy, desecreation of human remains, and hindering apprehension.