MADISON, WIS. ? Police accused a college student of faking her own disappearance Friday, saying she planted a knife in the marsh where she was found to make it appear she had been kidnapped.

“We don’t think an abduction occurred at all,” Madison Police spokesman Larry Kamholz said.

University of Wisconsin sophomore Audrey Seiler, 20, was found cold and dehydrated but otherwise unharmed Wednesday in a marsh, four days after she disappeared. She told police she had been abducted from outside her apartment about two miles away, but surveillance video showed her walking out of the apartment wearing only sweats.

Investigators also obtained a videotape from weeks earlier showing Seiler buying the knife, duct tape, rope and cold medicine that she claimed her abductor used to restrain her.

Assistant Police Chief Noble Wray said Seiler used her computer to search Web sites for information about Madison parks and the extended weather forecast. In addition, he said, evidence indicated someone had used the computer during the four days she was missing, and at least two witnesses said they had seen her walking freely in the city during that time.

Wray declined to speculate on Seiler’s motivation or her mental state; he said it was too soon to say whether she could face charges. Authorities are trying to construct a timeline of her movements, he said. Dane County Dist. Atty. Brian Blanchard declined to comment.

Seiler also reported an unexplained attack in early February, telling police someone struck her from behind and knocked her unconscious.

Police estimated costs for the intensive manhunt would exceed $70,000, said Melanie Conklin, a spokeswoman for Mayor David Cieslewicz.

Earlier Friday, Wray disclosed that Seiler changed her story about what happened. She said she had left her apartment building because she wanted to be alone and was kidnapped by a man with a knife elsewhere in Madison.

Detectives continued to pick apart Seiler’s story, and two hours later, Wray held another press conference to say police didn’t believe her.

Police said Seiler and her family were in an undisclosed location in Madison. “Dateline NBC” reported Friday night that Audrey Seiler was in a psychiatric facility.

Kamholz, the police spokesman, said he spoke with Keith Seiler for about an hour Friday after Wray’s announcement. He said Keith Seiler felt bad about what police and everybody else went through, but was happy to have his daughter back.

On Thursday, Wray had acknowledged to reporters that “there may be inconsistencies” in the case. But he said then that the hunt was still on for a suspected abductor, and police issued a composite sketch based on Seiler’s account.

AP Photo Madison, Wis., Police Department spokesman Larry Kamholz holds up examples at a news conference of what Audrey Seiler used to foil police with her alleged abduction. Assistant Police Chief Noble Wrayn revealed Friday that Seiler planned her abduction before disappearing last week from her apartment at 2:30 a.m.