Nolan Wells' state autopsy completed amid investigation into teen's death: Officials

The results of the autopsy have not yet been made public.

Nolan Wells' official state autopsy has been completed, according to officials familiar with the investigation into the Mississippi teenager's death.

The results of the autopsy, conducted by the State Medical Examiner's office in Mississippi, have not yet been made public.

Once the investigation is complete, the case materials, including the autopsy report, will be presented to a grand jury, which will decide whether what happened to Wells involved a crime.

The 18-year-old college student vanished after going on a Fourth of July boat trip with friends to one of the Gulf Coast's barrier islands, officials said. Wells was last seen on Horn Island, a barrier island about 10 miles from the Gulf Coast, officials said. His body was recovered several days later.

A private autopsy commissioned by Wells' family preliminarily found that his cause and manner of death are "undetermined pending investigation," with the independent pathologist acknowledging multiple limitations in the report, the family's attorney said last week.

The Jackson County District Attorney's office has previously said it will present the case to a grand jury once the local sheriff's department investigation into Wells' death is complete. The DA's office said convening a grand jury does not mean there is any criminality and is standard procedure for most unnatural or suspicious deaths in the county.

Investigators are also poring over audio of a distressed phone call that one of Wells' friends made to a local towing company reporting their boat was "sinking" and in need of assistance -- a return trip which the friends have said Wells was not on. Investigators are doing their own analysis of the call in order to determine whether there may be any further clues gleaned, according to officials.

ABC News previously obtained the full audio recording of that call which includes the caller saying he wanted to "get this boat unsank and towed back," telling the dispatcher that everyone on board was unhurt and that "nobody here is over the age of 21." Ultimately, the company, Sea Tow, said its services were not needed because the boat found other help.

The wells family attorney, Ben Crump, told reporters on Thursday that his team has the audio tapes from the call and plans to retain consultants and audio experts to analyze them.