BOISE, Idaho — Six employees at a treatment center for people with severe disabilities have lost their jobs after an investigation concluded that some staffers physically and psychologically abused residents, Idaho’s welfare agency said Tuesday.

Two of the employees abused the residents at a unit of the Southwest Idaho Treatment Center in Nampa and four other employees knew about the abuse but did not report it, which is considered neglect, the Idaho Department of Health and Welfare said. They either voluntarily resigned or were terminated, the department said, declining to comment further.

Seven of the center’s 20 residents were abused, the investigation found.

The abuse was primarily psychological, resulting in bullying and insulting residents, said department spokeswoman Niki Forbing-Orr. However, the investigation found three incidents of physical abuse, including an employee slapping a resident and an employee applying inappropriate pressure on a resident’s jaw.

“These employees cannot work for health and welfare again,” Forbing-Orr said.

The department’s director, Russ Barron said in a statement that the work environment at the treatment center was challenging but “six employees engaging in this type of conduct is six employees too many.”

Department officials learned about the alleged abuse in June, when a center employee reported concerns about resident safety, said Forbing-Orr. The investigation covered the entire treatment center’s campus but officials focused their attention on one section of a building, she said.

The department said police were notified after the allegations surfaced. Authorities have since confirmed they have launched separate criminal investigations involving accusations of staff-on-resident abuse and neglect at the center. That investigation is still ongoing.

The center typically houses people with severe intellectual disabilities who are in crisis or who have significant behavioral challenges. The center’s goal is to provide treatment and care for residents so they can be moved to less-restrictive settings, like community-based group homes. But some of the residents have been there for years.

Formerly called the Idaho State School and Hospital, the center was the state’s only institution for the developmentally disabled for years. In 2009 state lawmakers began an unsuccessful push to close the facility amid budget cuts and a renewed focus on community-based care for those living with disabilities.

The facility was built in 1919 and once had more than 1,000 people living on a nearly 1-square mile (2.6-square mile) campus that resembled a working farm. Many residents were mentally ill, medically fragile or had behavioral problems in addition to developmental delays.

The center houses 20 residents and is staffed by 109 full- and part-time employees.