An autopsy found that the cause and manner of death of 18-year-old Nolan Wells, whose body was recovered near Mississippi’s Horn Island, remain undetermined.

The state medical examiner found two dark red-purple bruises beneath the scalp on the back of Wells’ head but found no external scalp injuries or skull fractures.

The findings matched a private autopsy commissioned by Wells’ family, which also classified his cause and manner of death as undetermined.

Wells disappeared after a July 4 boat trip with friends, and authorities said he appeared to have remained on the island after his friends left before his body was recovered two days later, ABC News has reported.

A grand jury recently found that criminal charges were not warranted at this point, while authorities continue to investigate the circumstances surrounding his death.