Civil rights attorney Ben Crump released information from a forensic examination of Nolan Wells’ cellphone as well as details of the official autopsy on Thursday, just days after a Mississippi grand jury said it found no evidence of criminal conduct in the teen’s death.

Attorneys representing the 18-year-old Black college student’s family have called for transparency, asking that the grand jury investigative materials and the official autopsy report be publicly released.

Crump and his team discussed the contents of the cellphone analysis, but they did not release a full report of all the messages sent and received in the days leading up to and the day of Wells’ death.

The grand jury had access to that information, including 282 pages of Snapchat conversations, when it convened last week, according to the panel’s report and Crump. Crump said the forensic examiner was able to track messages received and sent and tie them to the location of Wells’ phone from the day before he went missing all the way up to when his family got the phone back.

“The messaging, as I said, was very telling … some of his own friends were concerned about [how] people on Horn Island can be racist,” Crump said Thursday.

Wells’ family and their legal team have slammed the grand jury report and have been working to keep the investigation open and active. They’ve asked for federal authorities to look into the events surrounding Wells’ death. His body was found two days after he went with a group of mostly white friends on a boat trip to a barrier island for a 4 July party.

The high-profile death in a deep south state with a history of racial tension has sparked rampant speculation and suspicion. State and local officials and several of Wells’ white friends who had become the target of that speculation had hoped that the grand jury report would quell critics.

The grand jury report said the panel found Wells’ death to be “consistent with drowning” and found that he had not been in a fight or altercation while on the island.

Crump and Wells’ parents questioned how the panel could determine Wells probably drowned, when both the official and independent autopsies said the cause of death could not be determined.

The state’s official autopsy report, which Crump’s team received late on Wednesday, said Wells’ airways and stomach were empty, which they said raised questions about the grand jury’s finding.

“What this means is that there is no water in the stomach, there is no water in the lungs and there is no water in the throat,” Wells’ family attorney, Liza Park, said.

Both the official and independent autopsies noted fresh bruising on Wells’ head. A witness testified to the grand jury that he saw Wells slip awkwardly off the side of a boat around 3.30pm on 4 July, but that Wells continued to socialize after the fall and didn’t appear injured, the report said. The panel said it couldn’t determine whether the fall caused the bruising, but noted it was not a fatal injury.

Wells’ parents and their lawyers have voiced suspicions after Wells’ friends left the island without him, saying he wanted to stay behind and talk to a girl. Wells’ phone was on the boat that took him to the island, and his family and their attorneys have expressed doubt that he would choose to stay behind without his phone.

Andrew Garrett, the forensic examiner who extracted the contents of Wells’ phone, said the GPS and other phone data showed that Wells had opened it with his face while it was on the boat around 2.17pm. It was then locked and continued to receive messages as it traveled on the boat, then by car and eventually was picked up by his family.

A lawyer who represents some of Wells’ friends who have been the subject of speculation said it was unclear what new information the cellphone report revealed. “They never had the phone,” attorney Edward Paltzik said of his clients.

In a statement released after Crump’s Thursday news conference, district attorney Angel Myers McIlrath said she stood by the investigation.