SAN ANTONIO — A child psychiatrist fired over allegations that he sexually abused two residents at a state hospital for the mentally ill had been accused of sexually abusing patients several times during his 21 years working there, state officials said Thursday.

State investigators looked into all of the allegations of sexual abuse involving Dr. Charles Fischer when they were made, but they found no confirmation of abuse until last month, said Patrick Crimmins, a spokesman for the Texas Department of Family Protective Services. Fischer was fired Monday from the Austin State Hospital, where he worked in a supervisory role at the Child-Adolescent Psychiatric Services Unit.

Austin police said Thursday that Fischer, 59, is under investigation but has not been charged. He did not immediately respond to a phone message left Thursday at his Austin home, and it was not clear whether he had an attorney.

State officials declined to release even the most basic details of the allegations against Fischer, including how many people accused him of sexual abuse and how old they were when the alleged abuse occurred.

“We are all heartbroken over these allegations. We’re investigating the situation and considering our next actions,” Texas Department of State Health Services spokeswoman Carrie Williams said. “These kids come to us to heal, and the situation is very sad and extremely troubling for everyone involved.”

Disability Rights Texas, a federally funded nonprofit tasked by the government to help monitor state facilities for the mentally ill and disabled, said its records indicate there have been as many as eight allegations against Fischer. Beth Mitchell, an attorney for the organization, said there is indication the allegations go back a decade.

Mitchell said her organization is now trying to uncover why previous allegations against Fischer were unfounded.

Mitchell said that while she doesn’t believe the state’s standard for “confirming” an allegation is too high, she said investigations commonly end with the alleged victim being discredited.

Mitchell said Fischer has never popped up on her organization’s radar before.

Fischer had worked since 1990 at Austin State Hospital, which is part of a system of 11 state hospitals for people with mental illnesses. Crimmins said state caseworkers have received “several reports alleging sexual abuse by Dr. Charles Fischer dating back several years,” but would not elaborate.

Last year, state investigators confirmed 39 cases of sexual abuse in facilities that are either state-run or contracted by the state. Yet investigators “confirming” an allegation of abuse are rare: Fewer than 2 percent of more than 2,100 abuse allegations made in state psychiatric hospitals in 2010 were confirmed by the state.