Detective Inspector Greg Williams said an item likely used in the deaths had been recovered, but would not confirm if it was a knife.
"Dasha has suffered quite a severe wound to her neck area and there is some suggestion of some form of sexual assault," Mr Williams said.
"Certainly the neck injury appears to be a significant cause of death.
"In the case of Frandi, he has self-inflicted wounds to his left wrist which is most probably the cause of his death."
Police said a driver had spoken to Miss Pytlickova at the Deadmans Point Bridge at about 2pm on Saturday, but was unable to pick her up as he was heading in another direction.
They wanted to hear from anyone who had seen her trying to hitch a lift or eating a meal at Cromwell, Omarama, Kurow or Waimate on Saturday afternoon.
Mr Williams said Miss Pytlickova's backpack and small shoulder bag containing personal items, including a notebook computer, had been found in Frandi's BMW.
The movements of the pair were still being traced, but police believe Miss Pytlickova was still "alive and well" up to about 6.40pm on Saturday.
It was possible Frandi was alive for "a period of time" after Miss Pytlickova's death.
Frandi was being sought by Waimate police in relation to other criminal allegations when he went missing on Saturday, and Mr Williams said the proper routines were followed.
The family of Miss Pytlickova, including her sister who is New Zealand, were having great difficulty coping with what had happened and were focused on getting her body home.
The deaths of Frandi and Miss Pytlickova will now go to the coroner.