OCEAN SPRINGS, Mississippi. — The family of Nolan Xavier Wells is still searching for answers about what exactly led to the 18-year-old elite athlete’s death during a Fourth of July boat trip with friends on the Mississippi Gulf Coast.

Although Wells traveled by boat with his friends to Horn Island, he did not return to the group that afternoon as planned. His body was found two days later off the coast of the island.

An independent autopsy commissioned by the family was inconclusive, civil rights attorney Ben Crump announced Wednesday, and the Mississippi sheriff’s department investigating Wells’ death has not made a public statement about the case in recent days.

Wells’ parents say the tragedy is plagued by conflicting stories and missing details. That mistrust has been deepened by the state’s long legacy of racism. Wells was the only black person in the group that day; everyone else on the tour was white.

Here’s a look at what is known and what’s next in the search for answers.

Wells’ mother, Christine Wonsley, became concerned when one of her friends called around 11 p.m. on the Fourth of July. After trying to locate her son on her own, she reported him missing to the police. One of Wells’ friends had also reported her missing to the United States Coast Guard.

Wells did not make it back to the mainland, but he did make it back to his phone and car keys. Wonsley used an app to track Wells’ phone and, after a friend went to where it was on the ground to pick it up, he noticed that some of his messages appeared to have been deleted. Wells’s father, Elmore Wonsley, went to get his son’s keys to the ship, which were in the house where Wells had stayed with his friends the night before his trip. She said her son’s car was still parked in the yard.

The day after Wells’ body was found, Jackson County Sheriff John Ledbetter said Wells’ friends were cooperating with authorities and that investigators did not suspect foul play. Ledbetter said people interviewed by investigators said Wells decided to stay on the island assuming he would return to the mainland with someone else.

Crump said bystander video from the island showed a person he believed was Wells arguing with someone to give him back his phone. Crump said another witness reported that Wells had planned to leave on the boat with his friends.

The independent autopsy report showed no evidence of fractures or deep tissue injuries, and described a “red discoloration” on the back of Wells’ skull as “inconclusive” and warranting further investigation, Crump said.

Dr. Robert Mitchell, the forensic pathologist who performed the autopsy, wrote in the report that he could not rule out the possibility that “non-accidental factors contributed to or caused the death.” He called the cause of death “undetermined” pending further investigation.

The autopsy was complicated by some factors. The body had decomposed and had already undergone an autopsy, meaning the organs, including the lungs and neck structures, had already been removed. That’s not an unusual practice for autopsies, but it makes it impossible to determine whether Wells had a neck injury or whether water had entered his lungs, according to Mitchell’s report.

Crump has asked state officials to provide that evidence for the family to review.

The Mississippi medical examiner has not released the results of the state autopsy and did not respond to messages left Wednesday requesting a timeline for when those results would be released.

Toxicology tests can often take weeks, and those results have also not been released yet.

Attorneys for the family said they spoke with the prosecutor last week about procedural issues, but said sheriff’s department officials have not shared any updates on the investigation’s findings in the days since Wells’ body was discovered.

Crump said he is working with the local prosecutor to inspect Wells’ phone. The prosecutor agreed to present the results of the investigation to a grand jury once it is complete, according to Crump.

The Jackson County Sheriff’s Department has been requesting videos, photographs and first-hand accounts from people who were on the island. But the sheriff’s department has not made any public statement about the investigation in more than a week.

The Rev. Al Sharpton, who gave the eulogy at Wells’ funeral, has promised a $100,000 reward for any new information about the circumstances surrounding Wells’ death. Half of the sum will be covered by actor and producer Tyler Perry, who also paid for the funeral, Sharpton said.

Wells’ death has sparked rampant speculation and suspicion as people grapple with Mississippi’s history of racial tension and what it means to be a black person in a majority-white space.

Sharpton invoked Mississippi’s history of racist violence during his eulogy, including the lynching of Emmett Till and the murder of Medgar Evers. He told law enforcement authorities: “Before we can medicate and cure today, we have to look at your history.”

Former NFL quarterback Colin Kaepernick paid for the independent autopsy. Other celebrities have lent support to Wells’ family, including filmmaker Spike Lee and former NFL player Terrell Owens, along with many prominent members of the black clergy.

The independent autopsy findings were announced to a standing-room-only crowd at the NAACP’s annual National Convention in Chicago.

Wells’ parents described him as a peacemaker who avoided confrontation, and his football coach at Southwest Mississippi Community College said the receiver was outgoing and the type of person who never met a stranger.

Crump says many things about the case don’t add up: Why would a teenager leave a phone behind if he plans to stay on an island? Why didn’t anyone see Wells drown or a person struggling in the water? Why did one witness report that Wells planned to leave on the boat with his friends, while others apparently told the sheriff that he had decided to stay?

Horn Island is uninhabited and accessible only by boat, an 11-mile (18-kilometer) spit of land near the Alabama state line. Crump said about 200 people were there on the Fourth of July. The family hopes witnesses will come forward to help fill in the blanks about what happened before Wells entered the water.