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A brigadier general admits he committed one military crime: carrying on a three-year adulterous affair with an underling.

But when his court-martial opens Tuesday, Jeffrey Sinclair will be fighting to prove that he didn't force his ex-lover to perform oral sex or threaten to kill her — accusations that could send him to prison for life if he's convicted.

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In the absence of physical evidence, the case that will play out in a Fort Bragg courtroom is likely to come down to a question of credibility.

Sinclair's lawyers have already alleged that his accuser, a captain who worked under him in Iraq and Afghanistan, has perjured herself on the stand.

The defense says the lead prosecutor stepped down after questioning her believability and that senior officers stopped him from cutting a plea deal.

Military prosecutors have not commented on the specifics of the case, but they charged Sinclair, 51, with forcible sodomy, indecent acts and conduct unbecoming an officer. They gave the captain immunity against adultery charges.

The trial will take place amid debate over how the military handles sexual assault allegations and whether commanders or prosecutors should have the power to decide which cases go to trial.

Brigadier General Jeffrey Sinclair, a U.S. Army general facing charges of forcible sodomy and engaging in inappropriate relationships stemming from allegations that got him sent home from Afghanistan this year, is seen in this handout photo received Sept. 26, 2012. U.S. Army via Reuters

The Associated Press contributed to this report.