WASHINGTON—Navy criminal authorities are investigating whether two members of the elite SEAL Team 6 strangled an Army Green Beret in June while they were in Mali on a secret assignment, military officials say.

Staff Sgt. Logan Melgar, a 34-year-old veteran of two tours in Afghanistan, was found dead on June 4 in the embassy housing he shared in the Malian capital, Bamako, with a few other Special Operations forces assigned to the West African nation to help with training and counterterrorism missions.

The Navy SEALs’ potential involvement also raised the prospect of a highly unusual killing of a U.S. soldier by fellow troops.

Melgar’s superiors in Stuttgart, Germany, almost immediately suspected foul play, and dispatched an investigating officer to the scene within 24 hours, military officials said. Agents from the Army’s Criminal Investigation Command arrived soon after and spent months on the case before handing it off last month to the Naval Criminal Investigative Service.

No one has been charged in Melgar’s death, which a military medical examiner ruled to be “a homicide by asphyxiation,” or strangulation, said three military officials briefed on the autopsy results. The two Navy SEALs, who have not been identified, were flown out of Mali shortly after the episode and were placed on administrative leave.

“NCIS does not discuss the details of ongoing investigations,” Ed Buice, the agency’s spokesperson, said in an email, confirming that his service had taken over the case on Sept. 25.

Neither the Army nor the military’s Africa Command issued a statement about Melgar’s death, not even after investigators changed their description of the two SEALs from “witnesses” to “persons of interest,” meaning authorities were trying to determine what the commandos knew about the death and if they were involved.

The uncertainty has left soldiers in the Green Beret community to speculate wildly about any number of possible motives, from whether it was a personal dispute among housemates gone horribly wrong to whether Melgar had stumbled upon some illicit activity the SEALs were involved in, and they silenced him, according to interviews with troops and their families. Other officials briefed on the inquiry said they had heard no suggestion that the Navy commandos had been doing anything illegal.

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