Investigators ruled Melgar's death a homicide by strangulation and, a recent report in The Daily Beast cited five sources in the special-operations community as saying the SEALs killed Melgar after he discovered they had illegally pocketed money used to pay informants.
Lawrence Brennan, a former US Navy captain and an expert on naval law, told Business Insider that although the Navy has not executed a sailor in more than 150 years, this case was extraordinary.
"If the reported facts were established, the murder of Staff Sgt. Melgar would be among the most aggravating factors and could justify referral to courts-martial as capital cases," Brennan wrote to Business Insider.
According to the law, "the death penalty is available in cases of pre-mediated murder, as appears possible in this case," wrote Brennan.
Brennan said the SEALs could stand before the military equivalent of a grand jury, where capital punishment would be on the table.
Melgar, a 34-year-old Texan, deployed to Afghanistan twice. He was assigned to Mali with the 3rd Special Forces Group to help train locals and support counterterrorism operations.