At a media conference this afternoon, Mr Williams said it was likely Dasha had been abducted and driven to an isolated area where Frandi had attempted to have sex with her and a struggle had followed.
Police do not believe anyone else is involved but want to speak to anyone who gave her a lift that day.
"It is also likely that Dasha went to a cafe or takeaway during her journey between Cromwell and Kurow.''
She was carrying a 60-litre blue/grey backpack.
"Dasha's family in the Czech Republic have been informed and say they are shocked and devastated about what has happened. They are still coming to terms with the news and have requested privacy,'' Mr Williams said.
Today police also found Frandi's silver BMW car in trees off Kaiwarua Rd, about 3km from where the bodies were found.
The area had been cordoned off and a detailed forensic examination of the vehicle would be done.
Mr Williams also confirmed that Frandi was known to police and was given a three-and-a-half year prison sentence in 2000 for abduction of a 19-year-old woman for sex.
"What I would say is that what has occurred in this situation seems very similar to what occurred in 2000.''
Court staff confirmed that as well as the kidnapping conviction, Frandi was also convicted and fined for common assault in 2005, and for cultivating cannabis and minor traffic offending in 2006.
Mr Williams said Frandi was also under investigation for allegations of child molestation after police received several complaints and that will be an aspect of the inquiry as well.
Asked if Frandi was being monitored by police as a result of concerns about him, Mr Williams said: "I really can't comment on what Waimate police have been doing here. Clearly they were aware of his history, but I don't think there would be any specific surveillance of any nature once he has been released from prison.''
He said although police had made positive progress today, there was still much work to be done.
Speaking from the Czech Republic Embassy in Canberra, the Czech ambassador to Australia, New Zealand and the Pacific Islands Hynek Kmonicek said Dasha's family had been contacted by consulate staff.
The embassy would do anything it could to help New Zealand authorities.
"If the New Zealand authorities want anything from the Czech Republic then of course we will immediately provide it.''
Dr Kmonicek was unsure what arrangements had been made for the body at this stage.
News of the death had not yet been picked up by Czech media, but he was sure it would be soon.
Due to differences in media laws, it was unlikely her name would be published there.
A close friend of Frandi, who agreed to be interviewed on condition his name was not used, said the Waimate local came from a troubled background.
"He had a number of issues, he didn't talk too much about his family other than that there were problems there. He kept things to himself.
"He was a loner, basically. Somebody else has said exactly the same thing, and he was.''
His father, Arthur Frandi, a barman at the local town and country club, died of cancer a few years ago.
"Jason took it reasonably hard but I don't think that's the only problem. He comes from a troubled background.''
The two met when working in the forest when Frandi was a teenager.
"Once we got him into work he came right and he got bit more confidence in the team we were in and he became a good guy, he was a really good guy. We had no troubles with him.
"He was a very powerful individual - very strong - but he didn't use that against anybody, to my knowledge, but he certainly had that very physical presence. He was a very capable forestry worker, one that all the guys in our team looked up to. He sort of set the standard out there.''
Frandi used to retreat to the forestry block where his body was found on Sunday when he became angry, he said.
"When I look back he did have some problems regarding his family, and some other things. He used to get a bit upset sometimes so he used to go off on his own into the forest and then come back some time later and he'd be okay. But he did have moments.''
The friend said he had tried to nurture Frandi when he was a troubled teenager.
"I did take him under my wing to some extent when he was younger and I felt he sort of came right when he had a good job.
"I feel a bit sad that I didn't pick up something when I saw him last week, but you can't look at things in the past tense.''
