Correction: An earlier version of this story incorrectly described the status of legislation, sponsored by Sen. Claire McCaskill (D-Mo.), that would remove military commanders’ ability to overturn sexual-assault convictions and would require a dishonorable discharge as a minimum sentence for any service member convicted of sexual assault. That measure was signed into law last December. It is a different McCaskill-sponsored measure, which would grant  additional rights to victims, that awaits House action after being passed by the Senate this March. This version has been corrected.

An Army staff sergeant is accused of sexually assaulting several female soldiers since 2011, including at least one while he was deployed to Afghanistan and others more recently while he served as a drill sergeant, according to military officials and court documents.

The accusations are detailed in a charging document filed against Staff Sgt. Angel M. Sanchez, who appeared at a pretrial hearing at Fort Leonard Wood in Missouri on Wednesday, a proceeding that could lead to a court-martial later this year. Sanchez has served at the base since August, training new soldiers with the 14th Military Police Brigade.

The Pentagon said this month that it received thousands of reports of sexual assault last year, and the problem is much more widespread than commanders had realized. The case against Sanchez is singular because he is alleged to have assaulted a dozen women, and he used his position as a drill sergeant to threaten some of his alleged victims, according to military documents.

Ernesto Gapasin, Sanchez’s attorney, said in a phone interview that his client was formally notified of the charges by his commanding officer at Fort Leonard Wood on May 13. Several of the women involved in the case testified at the hearing Wednesday, and Gapasin said he had questions about the reliability of some of them.

“In my opinion, there are a lot of issues with the credibility of the witnesses and the government’s case against my client,” he said.

Sanchez has served one deployment each in Iraq and Afghanistan, earning a Bronze Star, Army officials said. He has been removed from drill-sergeant duty, and currently serves in an office job with his unit, said Tiffany Wood, a spokeswoman at Fort Leonard Wood.

In one incident that occurred sometime between Sept. 17 and Jan. 31, Sanchez grabbed a female soldier by her hair and forced her to perform oral sex in a women’s bathroom in the barracks at Fort Leonard Wood, military prosecutors allege in the charging documents.

Sanchez allegedly committed several other assaults in that time frame, authorities said, including one in which he placed a female soldier “in fear that she would be kicked out of the U.S. Army if she did not engage in sexual acts” with him, according to charging documents. In that case, he forced her to perform oral sex while in an office he shared with other drill sergeants at Fort Leonard Wood, military officials said.

Sanchez is accused of sexually assaulting four women and assaulting eight others by touching them inappropriately, said Wood, the base spokeswoman. The case has received little attention until now, but it could serve as further kindling in the long-burning debate about how sexual-assault cases should be handled in the military.

Sen. Claire McCaskill (D-Mo.), who represents Fort Leonard Wood, has been among the most vocal lawmakers in pressing for an overhaul of the military justice system when it comes to sexual-assault cases. In December, Congress passed a bill she sponsored that would remove military commanders’ ability to overturn sexual assault convictions, give victims their own independent lawyer and require a dishonorable discharge as a minimum sentence for any service member convicted. An additional law that grants even more rights to victims was passed in March by the Senate.

An official in McCaskill’s office said Tuesday that she is aware of the case and tracking it but that “it wouldn’t be appropriate to comment on it right now as the trial is ongoing.”

Sanchez’s alleged crimes date to when he was deployed to Afghanistan between March 2011 and March 2012, according to charging documents. At one point during that time, authorities said Sanchez raped a female service member in a temporary housing unit that had been set up for women on a base in eastern Afghanistan.

Sanchez also is accused of attempting to spy on one female soldier while she was showering in Afghanistan, and watching another naked female service member while she weighed herself in a closet, prosecutors say. Those incidents allegedly occurred at Outpost Dandar, in Kunar province.

While in Afghanistan, Sanchez also kept up a steady stream of obscene commentary aimed at his female colleagues, military prosecutors said.

“I know you guys are married, but it’s okay if you have a deployment buddy,” he allegedly told one lower-ranking soldier while raising the prospect of sexual contact.

“If you give me two minutes, it will be the best two minutes of your life,” he told another woman, according to the charging documents.

The case against Sanchez has similarities to a sex scandal at Lackland Air Force Base in Texas that erupted after a single complaint was filed in 2011. Dozens of female recruits were the victims of sexual assault or other crimes by their military training instructors, an investigation on the base later found.

Craig Whitlock contributed to this report.