A former Dorchester Municipal Court probation officer was set to be arraigned Wednesday on charges that he raped a probationer under his supervision earlier this year.

William Averill, 50, of West Roxbury, was indicted by a grand jury on three counts each of rape and indecent assault and battery, as well as one count of assault with intent to rape.

The officer was placed on administrative leave while under investigation for the attack, Boston police said.

Averill was assigned to supervise a woman in her 20s who was serving one-year probation on convictions for larceny and receiving stolen property, according to a statement from the Suffolk County District Attorney’s office.

When she arrived for a required Jan. 5 meeting with the officer, the victim told investigators he began to touch and kiss her while inside of his courthouse office.

Prosecutors said the woman asked Averill to stop, and he complied, but later pulled the shades to his office and sexually assaulted her.

The victim left the courthouse and later told a relative about the attack, which lead to a report and police investigation.

Authorities said they recovered DNA evidence that matched a sample provided by Averill, and excluded 99.92 percent of other men as possible contributors.