The mother of Mollie Tibbetts believes her daughter may have been abducted on July 18 and begged her possible kidnappers to let her go.
Previous reports indicated Mollie's red work shirt might have been missing, leading some to theorize she was taken in the morning not at night.
"I can't tell you how much we appreciate you", he said. It's the first major potential clue discovered in the search for Tibbetts, who hasn't been seen since July 18 when she left her boyfriend's home to go for a run.
Calderwood announced at a news conference that $172,000 and counting had been raised for a new "Bring Mollie Tibbetts Home Safe" reward fund.
Anyone with information in the 20-year-old's disappearance is urged to call Crime Stoppers of Central Iowa at 800-452-1111 or 515-223-1400.
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Jack has said that he believes Tibbetts would have had both her fitness tracker and cellphone when she went out for her jog. He said the group exists for people who can not come forward to police, including those who are guilty or involved in a crime. Donations can be made on the Crime Stoppers website, he noted. This is going to be solved by someone coming forward with information.
Part of the investigation involves a reported sighting of Tibbetts at a truck stop in Missouri, about 380 kilometres away from her hometown.
State investigators have said they pursue all leads and have conducted multiple searches.
Authorities have yet to give an official timeline; but police have been combing through information from Tibbetts' Fitbit, which she always wore, as well as her cellphone and social media accounts. Investigators have reached no conclusions about why she has disappeared.
Kevin Winker, investigative operations director for the Iowa Department of Public Safety, said he knows the tight-lipped approach is frustrating for people who are eager to know what happened to 20-year-old Mollie Tibbetts. She was last spotted jogging around 7:30 that evening, wearing gym shorts, a black sports bra and running shoes, the sheriff's office said.