Stephen Robinson, 56, is scheduled to be released from the Washington State Penitentiary at Walla Walla on Friday.
But Attorney General Bob Ferguson said Robinson remains a threat and should be held indefinitely at the state's Special Commitment Center on McNeil Island.
"Mr. Robinson has admitted to more than 100 heinous assaults on young girls and must not be released into our community," Ferguson said in a press release.
Robinson was convicted of sexually violent offenses against young girls in Benton County in 1984 and in Colorado in 1999. He told authorities that he would seek out and attack other young girls if released, Ferguson said.
The attorney general's office filed a petition Tuesday in Benton County Superior Court, a first step in seeking a civil commitment. A probable cause hearing could be held as early as Friday. If probable cause is found, Robinson will be transported to the Special Commitment Center pending trial.
The unit was established in 1990 following enactment of the state's sexually violent predator law, which permits the involuntary civil commitment of sex offenders who are likely to commit acts of sexual violence if released to the community.
As of April, there were 296 sexually violent predators civilly committed in Washington state.
The Tri-City Herald reported Wednesday that Robinson was convicted in 1984 in Benton County of indecent liberties after a 3-year-old girl reported to her father that her crotch area hurt and described abuse by Robinson.
"By Robinson's own current admission, he was having sexual intercourse with the toddler within days of meeting her, and that the molestations/rapes lasted more than six months," according to court document.
Robinson also was convicted of sexual assault of a child in Denver County, Colo., 15 years later. That case involved a 9-year-old girl who he gained access to through her prostitute mother, court documents said.
"Robinson traded sex with the girl for some drugs for the mother. He had done this before and had frequented prostitutes that had daughters between (the ages of) 4 and 8 for this purpose," the documents said.