SEATTLE -- The U.S. soldier accused of carrying out one of the worst atrocities of the Iraq and Afghanistan wars is due to appear Monday in a military courtroom, where prosecutors will for the first time lay out their case that he slaughtered 16 people, including children, during a predawn attack on two villages in the Taliban's heartland.

Staff Sgt. Robert Bales, a married father of two from Lake Tapps, Wash., is accused of slipping away from a remote outpost in southern Afghanistan early on March 11 with an M-4 rifle outfitted with a grenade launcher to attack the villages of Balandi and Alkozai, in the dangerous Panjwai district of Kandahar province.

The massacre left 16 dead, nine of them children, and 11 of them members of the same family. Six others were wounded, and some of the bodies were set afire.

A preliminary hearing, called an Article 32 hearing, begins Monday before an investigative officer charged with recommending whether Bales' case should proceed to a court-martial. The hearing is scheduled to run as long as two weeks. Part of it will be held overnight to allow video testimony from witnesses in Afghanistan.

Bales, 39, an Ohio native, joined the Army in late 2001, after the 9/11 attacks, as his career as a stockbroker imploded. An arbitrator entered a $1.5 million fraud judgment against him and his former company that went unpaid. Then his attempt to start an investment firm in Florida failed.

He was serving his fourth combat tour after three stints in Iraq, and his arrest prompted a national discussion about the stresses imposed by multiple deployments.

One of his civilian attorneys, Emma Scanlan, spent the past week at Joint Base Lewis-McChord to prepare for the hearing. She declined to say to what extent lawyers hope to elicit testimony that could be used for a mental-health defense.

Bales faces 16 counts of premeditated murder, plus other charges of attempted murder, assault and using steroids.

Bales himself will not make any statements, his lawyers said. During Article 32 hearings, defendants have the right to make sworn or unsworn statements. Making a sworn statement opens the defendant to cross-examination by the prosecutors.

No motive has emerged. Bales' wife, Karilyn, who plans to attend the hearing, had complained about financial difficulties on her blog in the year before the killings, and she had noted that Bales was disappointed at being passed over for a promotion.

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Another attorney for Bales, John Henry Browne, described those stresses as garden-variety -- nothing that would prompt such a massacre -- but has also said, without elaborating, that Bales suffered a traumatic incident during his second Iraq tour that triggered "tremendous depression." Bales remembers little or nothing from the time of the attacks, his lawyers have said.