Witnesses told investigators that 18-year-old Nolan Wells had been drinking heavily with friends on Horn Island in Mississippi, according to a document with preliminary information from the Mississippi Department of Marine Resources.

The document — a description sent on July 5 by the Marine patrol as part of attempts to find Wells after he went missing — was an email that listed basic information for Wells, including his physical description, as searchers scanned the island for signs of him after he went missing on July 4.

Wells was found dead on July 6 and his cause of death is not known.

The official autopsy report from the state Medical Examiner’s Office and the toxicology tests are still pending. A private autopsy commissioned by Wells’ family preliminarily ruled his cause and manner of death as “undetermined pending investigation.”

Authorities said they suspect Wells drowned.

Jackson County Sheriff John Ledbetter said there was no initial indication of a crime, but he stressed that investigators were “working diligently to determine exactly what occurred.”

Ledbetter also said the sheriff’s office welcomed the family’s independent investigation.

Another document ABC News obtained reinforced what friends told investigators about why Wells was not on the return trip on July 4 in the boat he took to Horn Island with his friends.

A police report from the Mississippi Department of Marine Resources said, “several friends that traveled to the island on the vessel with Nolan” told authorities “that when they left he was in the company of an unknown female and that he chose to remain at the island.”

Friends have said they did not abandon Wells but needed to return to shore because their boat was taking on water.

ABC News obtained GPS data from the boat Wells rode to Horn Island, which showed the boat set off for the island at 9:56 a.m. on July 4 and arrived at 11:14 a.m. The data showed the boat was “stationary” from that point until 4:30 p.m.

At 4:31 p.m., the boat left Horn Island, moving slowly at no more than 4.2 knots for nearly 3 miles. At 5:25 p.m., the boat “regains normal operation” with a speed of 30 to 35 knots and arrived on shore about 20 minutes later, according to the data.