An Army doctor has been under investigation for more than a year in a sprawling sexual assault case involving at least 23 alleged victims, including his patients, according to military documents obtained by The Washington Post and interviews with four people familiar with the case.

Maj. Michael D. Stockin, 37, could be charged within days, said a senior Pentagon official and two other people who spoke on the condition of anonymity to discuss an active criminal probe. The Army, in a statement, said Stockin was "suspended from seeing patients" in February 2022. He had been assigned as an anesthesiologist assigned to Madigan Army Medical Center at Joint Base Lewis-McChord in Washington state. The service would not address whether charges are imminent.

"The Army does not comment on ongoing investigations as a matter of policy," Cynthia Smith, a spokeswoman, said in a statement. "While we're limited in what we can say . . . the Army takes all allegations of sexual assault seriously - this includes investigating thoroughly, supporting victims, and holding offenders accountable when warranted."

People familiar with the case said additional victims could come forward with allegations. Based on the number identified by investigators thus far, this is one of the military's largest sex-abuse cases in recent memory. It underscores, too, the scope of what remains a pervasive problem within the Defense Department, as officials spanning multiple presidential administrations have struggled to protect personnel from accused sexual predators. A Pentagon report released in April said the military recorded 8,942 reports of sexual assault in the previous year despite recent reforms.

Stockin, reached by phone and asked if he was aware of the allegations, said that he had retained legal counsel and needed to consult his lawyer.

Stockin's attorney, Robert Capovilla, said in a separate phone call that the Army has "operated behind the wall of secrecy" for more than a year.

"We have certainly not been notified that any charges are pending, and I've been in touch with that legal office on several occasions," Capovilla said. "I would simply ask that everyone simply reserve judgment until he has the right to be heard, until his defense team is given all of the evidence, and until due process plays its course."

Stockin has been assigned to Joint Base Lewis-McChord, about 40 miles south of Seattle, since July 2019, though it is unclear if all of the alleged assaults occurred there. Official personnel records provided by the Army show that, over his 10-year military career, he has served in Iraq, at Tripler Army Medical Center in Hawaii and at Walter Reed National Military Medical Center outside of D.C.

A soldier and former patient of Stockin's who reported him to authorities said in an interview that he first encountered the doctor at Madigan Army Medical Center in January 2022, during a visit to the hospital's pain management clinic where he had sought treatment for a chronic lower-back injury. Stockin was personable during the appointment but surprised the soldier when he asked him to drop his pants, he recalled. The doctor felt the soldier's ankles and legs, asking if he could feel various touches, and eventually held the man's genitals, the soldier said.

"It felt wrong," the soldier recalled, saying the experience left him wondering whether the doctor's methods were legitimate.

The Post generally does not identify the victims of sexual assault. The soldier, an enlisted noncommissioned officer with more than 10 years of military service, had a follow-up appointment several weeks later in which Stockin, with another colleague in the exam room, administered an injection for back pain. When the soldier returned for a third appointment that spring, he was told Stockin was not seeing patients.

"The longer it went on," the soldier said, "the more it irked me. The longer I let it fester, the more I'm thinking, 'That wasn't right. If I'm keeping my mouth shut, this is going to keep happening.'"

The soldier said he consulted with his primary-care physician about what had happened and came away from the conversation certain that a doctor would never need to touch a patient that way to assess the effects of a back injury. The soldier said that he met last year with an agent from the Army's Criminal Investigation Division and was told by investigators recently that charges will be brought by the end of August.

Stockin also faced allegations of abuse in a divorce case, according to court documents filed in Pierce County, Wash. His wife sought a protective order against Stockin in December 2022, accusing him of verbal abuse, harassment and unwanted sexual contact during their marriage, the documents say.

Reached by phone, his wife said she became aware of the Army investigation after filing for divorce and declined further comment about the case.

"I did have a lot of love for him," she said, "but it just got to the point where I can't continue to be in this situation any longer."

It's unclear if Stockin has responded formally to his wife's allegations. When reached by The Post, he denied the claims. The divorce is pending.

Disclosure of the Army's investigation comes just weeks after President Biden signed an executive order directing that certain criminal cases, including those involving sexual assault, be moved from the purview of military commanders and assigned instead to independent prosecutors. The shift, which won bipartisan support in Congress, followed years of complaints that some military officials failed to treat the issue with the seriousness it warrants by going easy on sexual predators, allowing them to victimize multiple people and discouraging survivors to report assaults.

Josh Connolly, a senior official with Protect Our Defenders, a nonprofit that provides free legal assistance to survivors of sexual assault in the military, said the Defense Department has a demonstrably poor track record when it comes to protecting people from such crimes. The nature of military service, which requires personnel to move from facility to facility every few years, can enable serial offenders, he noted.

"I would be shocked," Connolly said, "if more people do not come forward."