"We do not believe there is a suspect at large, period," Assistant Police Chief Noble Wray said.
Surveillance video showed Audrey Seiler, a University of Wisconsin-Madison sophomore, walking out of her apartment about 2:30 a.m. Saturday wearing only sweats. She was found Wednesday in a marsh about two miles away, cold and dehydrated but otherwise unharmed.
Seiler told police her abductor used duct tape, rope and a knife against her.
But Wray said police obtained videotape of Seiler buying some of those items at a local store weeks earlier.
She also used her computer to search Web sites for information on Madison parks and the extended weather forecast,
Wray said the search of her computer also indicated someone had used it during the four days Seiler was missing, and at least two witnesses said they had seen her walking freely in the city during that time.
"It's the totality of the picture," Wray said.
Earlier Friday, Wray had disclosed that Seiler, who had also reported an unexplained attack in early February, had changed her story about what happened last Saturday. She said she was abducted by a knife-wielding man — but from somewhere else in the city, not from her apartment.
"Audrey stated that she just wanted to quote, unquote, be alone," Wray said.
While citing inconsistencies, Wray said it was too soon to say whether Seiler could face charges. Authorities were still trying to construct a timeline of her movements, he said
Surveillance video showed the sophomore leaving her off-campus apartment alone about 2:30 a.m. on Saturday. She was found Wednesday in a marsh about two miles from her apartment.
Her return ended an intense search in which dozens of volunteers from Seiler's hometown of Rockford, Minn., combed through marshes and woods around campus and investigators scoured phone records and apartments for clues.
It also touched off a fruitless hunt for her supposed kidnapper.
The story of her disappearance generated nationwide news coverage, and the attention continued with the case cloaked in mystery after her safe return.
By Friday morning, some were already questioning whether the abduction ever happened.
CBS News Correspondent Jon Frankel reports some in Madison say police may have been reluctant to call this a fabrication, because several years ago police accused a rape victim of fabricating her crime and then found her story to be true.
"We do not have the luxury of being able to speculate, draw conclusions, before an investigation is completed," Wray said at a second news conference Friday. "It would have been a disservice to the community, to the country, in this case, and also a disservice to the family for a professional law enforcement organization ... to jump to conclusions and assume that this was bogus."
A state Department of Revenue spokeswoman said a worker at the agency's building, which stands next to the marsh, was walking on a footpath on her lunch hour when she spotted Seiler and called police.
A high-level police source told CBS affiliate WISC-TV that the DOR worker must have talked to Seiler in the marsh. Seiler allegedly told the woman she was a college student and went the marsh to relax. The woman told the 911 dispatcher she also saw Seiler on Monday and Tuesday.
The Rev. Greg Fairow of Calvary Lutheran Chapel in Madison had visited with dozens of Seiler's family members and friends as they searched Madison's neighborhoods Tuesday and Wednesday before she was discovered. He said he had numerous intimate conversations with them and nobody ever mentioned anything that caused him to doubt Seiler's story.
"If there was a problem with Audrey that would have caused her to fabricate or manipulate, a possible reason would have come out ahead of time. Nobody told me anything."
The composite sketch released by police Thursday shows a white, clean-shaven man with a long chin, wearing a stocking cap. A caption describes the man as in his late 20s to early 30s. He has a stocky build and stands between 5-foot-10 inches and 5-foot-11 inches tall.
Police had declined to release the police report from a previous incident in which Seiler claimed she was attacked.
In that incident, Seiler said she was struck from behind and knocked unconscious Feb. 1 while she was walking near her apartment. Someone then moved her about a block, but she was not sexually assaulted or robbed, authorities said. The attacker wasn't found.
Police got their first chance to interview Seiler at length Thursday. Spokesman Larry Kamholz said she was cooperative and police had no reason to doubt she had been kidnapped.
She had spent Wednesday night with her family at an undisclosed location after her release from the hospital.
"We wanted to give her time to refresh, time to spend with her family," Wray said Thursday.
When she was found Wednesday afternoon, officers with guns drawn surrounded the marshy area looking for the suspect. Officers were back at the scene Thursday looking for clues, with the area cordoned off by police tape and several squad cars nearby.