A couple whose bodies were found in a shallow grave in southern Georgia were buried alive, and four people face murder and other charges, police said Thursday.

The official cause of death for Carol and James Sumner, both 61, of Jacksonville (search), was mechanical asphyxiation, said Ken Jefferson, a spokesman for the Jacksonville Sheriff's Office.

"In essence, it means they were buried alive," Jefferson said. Officials have not released any details on the condition of the bodies, including whether they were bound.

Family members reported the couple missing July 10. Then a former neighbor of the couple, Tiffany Cole, 23, was arrested in South Carolina along with two young men after the three allegedly used the Sumners' ATM card.

Authorities said information from them led to the arrest Friday of Bruce K. Nixon Jr., 18, of Macclenny. Police said he told them he abducted the couple, killed them and buried them in Georgia. The bodies were discovered Saturday.

Nixon has been held without bond in the Duval County Jail (search) on charges of murder, kidnapping and robbery. Cole, Michael J. Jackson, 23, and Allen Wade, 18, were arrested on charges of financial fraud, and also face murder charges in Jacksonville. They were being held in the Charleston (S.C.) County Jail.

There was no information immediately available on whether the four have lawyers.

The Sumners lived down the street from Cole in Ladson, S.C., until they moved to Jacksonville in February. Family members also said Cole had purchased a car from the Sumners. It was located near a hotel in Ladson, where Cole, Jackson and Wade were arrested.