NEW YORK — A week ago, 18-year-old Nolan Xavier Wells took a boat trip with friends to celebrate the Fourth of July on an island off the Mississippi Gulf Coast. He never returned.

Two days later, he was found dead. What happened, Wells’ parents say, is a mystery rife with conflicting stories, implausible explanations and missing details. It’s a case overshadowed by the state’s tense racial history and lingering distrust of law enforcement.

At a news conference Friday in New York City, Christine and Elmore Wonsley called for a thorough and transparent investigation into their son’s death, skeptical of claims that Wells told his friends to leave the island without him and suggestions that he, an elite athlete who could swim, had accidentally drowned.

Wells’ body was found early Monday along the shore of Horn Island, about 7 miles (11.2 kilometers) off the Mississippi coast, more than a day after he was last seen alive. The approximately 17.7 kilometers (11 mi) long spit of land is near the Alabama state line. The island is uninhabited and can only be accessed by boat. About 200 people were there on July 4, the family’s attorneys said.

“We just want to know what happened and why our baby didn’t come home,” Christine Wonsley said, looking up several times as she stood next to her attorney, Ben Crump, and the Rev. Al Sharpton, who will officiate at Wells’ funeral.

Crump said Wells’ family has commissioned an independent autopsy, performed by a forensic pathologist in Washington, D.C. with no ties to Mississippi authorities, while they await the results of an official autopsy, which could take weeks. They also plan to employ experts to recover messages that appeared to have been deleted from his cell phone, Crump said. They will eventually turn the device over to authorities, he said.

Wells’ family also encouraged witnesses to come forward and asked people to submit any video they recorded that may show him on Horn Island, echoing a call from the Jackson County Sheriff’s Office to help shed light on the moments leading up to Wells’ disappearance and death.

A photo posted on social media, purportedly from the boat trip to the island, shows Wells hugging three white male friends. Sheriff John Ledbetter said Wells’ friends were cooperating and investigators do not suspect foul play. Crump said those friends now have attorneys and that his investigators have not attempted to speak with them yet.

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 largely white space.

Actor and producer Tyler Perry is helping pay for Wells’ funeral, former NFL quarterback Colin Kaepernick is helping pay for his independent autopsy, and filmmaker Spike Lee showed up at the press conference to show his support for Wells’ family.

Crump said Wells’ parents hired him to conduct an independent investigation into their son’s death because they don’t trust law enforcement officials to conduct a fair investigation in a state still reckoning with its Jim Crow past, including the lynching of Emmett Till in 1955 and the murders of three civil rights workers in the 1960s.

“Mississippi history is something you don’t just read in books,” Crump told reporters at the Sharpton National Action Network headquarters in Harlem. “It is a lived experience of many African Americans that many times, when our children are murdered in very questionable situations, there is this notion that ‘Oh, there was nothing wrong, there was no foul play, let’s just sweep it under the rug.’ Well, we refuse to sweep it under the rug.”

It is the second case Crump has taken on in the state in recent months. He was also recently held by the family of a 1-year-old Mississippi boy who was killed when police shot at a moving car.

Ledbetter told The Associated Press this week that investigators suspect Wells “chose to stay on the island assuming he was going to return to the mainland with someone else.”

But Wells didn’t have his cell phone or keys, his friends did.

“What teenager would leave their phone behind if they were going to stay on this island? What teenager wouldn’t take their phone?” Crump said. “It doesn’t add up at all.”

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

“The friends come back and he stands there with a story about how he said to leave him behind,” Sharpton said. “But then, magically, one of the friends has his keys and his phone.”

The sheriff did not respond to messages from The Associated Press seeking his response to the family’s concerns.

Wells’ mother, Christine Wonsley, said she began to worry when a friend of hers called her shortly after 11 p.m. on July 4.

After trying to locate him on her own, she reported him missing to police and went with her husband to meet an officer in the parking lot of a McDonald’s, she said, a process exacerbated by a dispute over which law enforcement agency had jurisdiction over the island. One of Wells’ friends had also reported her missing to the United States Coast Guard.

Wells’ father, Elmore Wonsley, said he went out on a boat the morning of July 5 looking for his son near Horn Island. Teams from multiple local and state agencies began an extensive search and his body was recovered early Monday morning, family members confirmed.

“If he’s drowning, no one sees him drown? No one offers help? No one tries to help? I mean, obviously he stands out,” Crump said. “I think he’s the only black person I saw while watching the videos.”

Christine Wonsley said she used an app to track her phone and, after a friend went to where it was on the ground to pick it up, she noticed that some of her messages appeared to have been deleted. Wells, a social and family event photographer, had two Snapchat accounts, but neither of them had saved photos or messages, she said.

While searching for his son, Elmore Wonsley went to get Wells’ keys to the house where he stayed with his friends from the boat the night before their trip to the island. She said her son’s car was still parked in the yard.

Wells, who would have turned 19 next month, played wide receiver on the football team at Southwest Mississippi Community College in Summit, Mississippi, and had aspirations of playing at a high-level Division I program.

His trainer, Les George, told WAPT-TV that Wells “was a guy who never had a bad day. Ever.”

“He was very sociable with everyone, he didn’t know any strangers,” George said. “He would show up at my office and sit on the couch just to hang out and talk.”

Christine Wonsley said she and her husband educated Wells in history and talked with him about how to handle the racial tensions that still permeate the South.

Wells was a peacemaker who didn’t like division, once dancing while still in diapers to ease tensions while his parents argued, they said. He wanted everyone to be included and avoided confrontation.

“Nolan is a person with a big heart,” Elmore Wonsley said.

Wells’ parents said they last saw him the night before the boat trip. He came home, baked them salmon for dinner, and hugged his mother goodbye.

As people mourn and protest Wells’ death, Christine Wonsley urged them to follow her example.

“Please be peaceful,” he said. “Nolan wasn’t someone who liked fights, physical fights. He didn’t even like arguments. Don’t go out there trying to be tough. Think about what Nolan would want, and he wouldn’t want that kind of behavior.”