Nearly three weeks after 18-year-old Nolan Wells disappeared during a Fourth of July boating trip to Mississippi's Horn Island, investigators continue working to determine exactly what happened.

Authorities have not released Wells' official cause or manner of death, and toxicology results remain pending. Meanwhile, the case has drawn national attention as Wells' family, their legal team and law enforcement continue searching for answers.

Here's a timeline of the key developments in the investigation.

July 4: Wells disappears during boating trip

Wells traveled to Horn Island with a group of friends to celebrate the Fourth of July. According to GPS data obtained by CBS News from the Mississippi Department of Marine Resources, the boat departed around 9:56 a.m. and arrived at the island shortly after 11 a.m.

Authorities and those who were with Wells have said he was last seen around 3 p.m. The boat departed the island around 4:31 p.m. without him, and Wells was reported missing later that night after he did not return home.

July 5-6: Search ends with tragic discovery

Multiple local, state and federal agencies searched the waters around Horn Island before Wells' body was discovered on the morning of July 6 near the island's northwestern tip. His family later confirmed his death.

July 7: Family hires Ben Crump

Days after Wells' body was recovered, the family retained civil rights attorney Ben Crump, who announced his team would conduct an independent investigation while seeking the release of investigative records, witness statements and autopsy findings. Wells also underwent an official autopsy that day.

July 8-15: Investigation expands

Over the following week, Wells' family publicly questioned whether he would have voluntarily remained on the island after the group departed. Crump announced plans for an independent autopsy and later confirmed his team would conduct a mutual inspection of Wells' cellphone with investigators.

Jackson County District Attorney Angel Myers McIlrath also confirmed the case will be presented to a grand jury once the Jackson County Sheriff's Department completes its investigation, describing the process as standard procedure for most unnatural or suspicious deaths in the county. During that time, authorities also confirmed the FBI was assisting with the review of digital evidence collected during the investigation.

July 16: Boat audio released

Audio obtained by NBC News through a public records request captured someone aboard the boat calling a private towing company on July 4 to report the vessel was taking on water. The recording became part of the growing public timeline surrounding Wells' disappearance.

July 20-21: Funeral held, reward announced

Family, friends and community members gathered in Ocean Springs to celebrate Wells' life. During the funeral, Rev. Al Sharpton announced a $50,000 reward for information leading to an arrest and conviction in the case. Tyler Perry immediately pledged a matching $50,000 contribution, bringing the total reward to $100,000.

The following day, former NFL wide receiver Terrell Owens announced an additional $25,000 contribution, increasing the reward to $125,000.

July 23: Independent autopsy findings released

Crump announced preliminary findings from the family's independent autopsy, which was performed by Dr. Roger A. Mitchell Jr., a board-certified forensic pathologist and former chief medical examiner for Washington, D.C. The preliminary report concluded that Wells' cause and manner of death remain undetermined pending investigation, and that his date of death could not be determined.

According to Crump, Mitchell said the body's advanced decomposition and limitations caused by the earlier state autopsy prevented him from reaching a definitive conclusion. While the report found no lacerations, skull fractures or other significant traumatic injuries, Mitchell said foul play cannot be ruled out based on the available evidence. He also identified several unanswered questions, including how Wells entered the water, whether there were injuries to the neck, whether water was present in the airway and what toxicology testing will ultimately reveal.

Investigation continues

The Jackson County Sheriff's Department continues to investigate Wells' death and has repeatedly asked anyone with information, photos or videos related to the case to come forward.

The investigation has also drawn widespread national attention. Along with advocacy from attorney Ben Crump and Rev. Al Sharpton, legal analyst Nancy Grace has dedicated coverage to the case as questions surrounding Wells' death continue.

Investigators have reportedly interviewed more than 60 witnesses, and authorities have not publicly released the official autopsy findings. Toxicology results also remain pending as officials work to determine exactly what happened to the 18-year-old.

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