No one has been charged in Sergeant 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. The biggest unanswered question is why Sergeant Melgar was killed. “N.C.I.S. does not discuss the details of ongoing investigations,” Ed Buice, the agency’s spokesman, said in an email, confirming that his service had taken over the case on Sept. 25. Neither the Army nor...