FORT STEWART | An Army soldier confessed that he killed his pregnant wife by persuading her to wear handcuffs during sex and then suffocating her with a plastic bag over her head, a former Army buddy testified before a court-martial Monday.

Prosecutors at Fort Stewart used testimony alleging the confession to open their case against 22-year-old Pvt. Isaac Aguigui, who is charged with murder as well as killing an unborn child. He faces an automatic life sentence if a military judge convicts him of murder in the July 17, 2011, death of Sgt. Deirdre Aguigui.

Capt. Janae Lapir, an Army prosecutor, said in her opening statement Monday that Isaac Aguigui wanted to be free from a rocky marriage and coveted the $500,000 in life insurance and benefit payments he received from the Army after his wife was found dead in their apartment on the southeast Georgia Army post. She called him "a schemer" who tricked his wife into letting him handcuff her.

"Sgt. Aguigui never had a chance to fight back because she never saw it coming," Lapir said.

Civilian prosecutors say Aguigui used the insurance money to buy guns and bomb components for an anti-government militia group he started by recruiting other disgruntled soldiers. Aguigui pleaded guilty in a civilian court last summer to murder charges in the slayings of a former soldier and his girlfriend eight months after his wife died. Civilian prosecutors say he ordered their slayings to protect the group.

Aguigui is already serving a sentence of life without parole at a Georgia prison.

Friends of the Army couple testified Wednesday about constant fighting in their marriage over Aguigui's drug use and infidelities by both husband and wife. Deirdre Aguigui, 24, was about seven months pregnant when she died, and friends said her husband had questioned whether the child was his.

Testimony in pretrial hearings showed the Army was delayed in bringing charges because the military's autopsy failed to identify a cause of death for Deirdre Aguigui. Last year, a Georgia state medical examiner reviewed the case and gave a second opinion, saying she must have been choked or suffocated because every other potential cause could be ruled out. He noted marks on her wrists indicated she struggled violently as her hands were cuffed behind her back.

Aguigui's friend Michael Schaefer testified that Aguigui at first told him his wife died from a blood clot. About a month later, after they had been up all night using cocaine, they got into an argument. Schaefer said he asked his friend point-blank what really happened to his wife.

"He told me he had strangled her with a bag," Schaefer said. "He handcuffed her, put a bag over her head and strangled her" while also sexually assaulting her.

Capt. Scott Noto, one of Aguigui's defense attorneys, noted that Schaefer never mentioned a confession during several previous interviews with Army investigators or when he testified at a pre-trial hearing for Aguigui last summer.

Schaefer said he was afraid to speak up until Army prosecutors granted him immunity from prosecution in Deirdre Aguigui's death.

On Dec. 5, 2011, fishermen found the bodies of former Army Pvt. Michael Roark and his 17-year-old girlfriend, Tiffany York, in the woods of rural Long County near Fort Stewart. Both had been shot in the head.

Investigators arrested Aguigui and three other soldiers - Sgt. Anthony Peden, Pvt. Christopher Salmon and Pfc. Michael Burnett - and charged them in the deaths about a week after the bodies were found. Aguigui pleaded guilty July 19. Salmon and Peden, who prosecutors say fired the killing shots, are still awaiting trial.