Three adolescent boys at a Wright County residential treatment center were sexually abused in multiple incidents by a female staff member, state investigators have concluded.

In early March, a new staff member at the Maple Lake Recovery Center engaged in a range of criminal sexual offenses involving three boys, ages 14 through 17. The offenses included pinching one child’s nipples, sitting on another boy’s lap and asking the children to engage in inappropriate touching. The employee also boasted of past sexual encounters and exchanged personal contact information with the boys on Snapchat, a social-messaging app, according to a recently released investigation by the state Department of Human Services (DHS).

The female staff member, who is not identified in the report, resigned on being confronted and has been disqualified from having further contact with people receiving social services through state-licensed programs.

This marks the second time in less than three years that state investigators have substantiated sexual abuse at Maple Lake Recovery Center, a 16-bed treatment center for adolescent boys struggling with addiction. In 2016, state investigators found that a staff member performed oral sex on two 17-year-old patients after giving them cigarettes and allowing them to stay awake overnight. The victims had a variety of disorders, including autism, anxiety and a history of chemical dependency, state records show.

Jessica Meyer, the facility’s program director, said the most recent offenses occurred on a single day in March and were independently reported by facility staff to the state. “We take any boundary concerns extremely seriously,” she said. When the incidents came to light, she said, “We followed up immediately. It was one staff member, one time, and it was addressed.”

After conducting 13 interviews with residents, family members and staff, investigators found that the alleged assailant “made out” with one of the children, age 17, for one to two minutes, and also “pinched” the child’s nipples.

At one point, the staff member sat on another child’s lap and asked him to grab her nipples. She also repositioned another child’s hand so that it was touching her clothed buttocks, the report said. Other youth at the facility received “follow requests” from the woman’s personal Snapchat account, the report said.

When confronted about the misconduct, the woman resigned immediately and left the premises. Then, bizarrely, she returned to the facility minutes later and attempted to covertly leave a handwritten letter to the residents with her personal contact information.

Roberta Opheim, the state ombudsman for mental health and developmental disabilities, said the recent report is “sickening,” and is a dramatic reminder of the vulnerability of children placed in state-licensed treatment facilities. Minnesota has about 120 residential treatment centers for children, with a total capacity of about 2,800 beds, state data show.

“These children are placed there for treatment,” she said. “That means they already have trouble in their lives, and are at an age when they are testing boundaries.”

The facility completed an internal review and determined that its policies and procedures were adequate but were not followed by the employee. The facility has provided additional training to all staff regarding appropriate behavior with patients, the state report said.

Both the facility and DHS officials declined to comment on whether the incident has been referred to law enforcement officials. The Wright County Sheriff’s Office did not return multiple calls Monday.