I was wondering where the 6 days came from too. Local LE may have called the closest FBI office on day 1 for advice. Just because the FBI isn't at a press conference doesn't mean they aren't involved.
The 6 Day time frame came from the IA DCI Press Folks informing the media. Still not sure when the DCI joined the case. Would definitely like to know! Maybe someone at the next press conference can ask?
FBI Joins Iowa Officials Search For Missing Student Mollie Tibbetts
(there are a few different ones for the same day saying the same thing)
Before that day, there is no video showing FBI in Brooklyn, is there?
Also there is the interview from the Sheriff on July 25th.
Sheriff: boyfriend and brothers of Mollie Tibbetts aren't suspects
"ABC: Still being characterized as a missing persons case
"Kriegel: It is the longest one we have been involved with yet.
We usually find our people within a couple of days, its usually just because they have left for a short period of time."
"Kriegel: Well it stands out because she is a girl from Brooklyn, Iowa and we want to find her.
We are going to work hard and naturally our local law enforcement got involved and we are going to do anything we can and we asked for help from the DCI and they asked for help from the FBI and everybody wants to work together to find her. I don’t know if it is signifcant or not you ask for help and people help you, at least here in Iowa."
In that interview he seems to say his staff took the report on 19th, worked for a couple of days expecting Mollie to turn up, when she didn't he reached out for help from DCI and the DCI in turn took however long it took to ask the FBI to join the case.
The Media were there on the 19th and they have done a good job filming from Brooklyn. They filmed the first day (July 20th) volunteer searches - Deputy Anderson (I think that was his name) from the Sheriff's dept provided media with what was happening. He went so far as to say the helicopter they hoped to use could not join the search until late afternoon because of cloud cover. No FBI filmed that day.
Over and over for the next several days the media kept reporting they were asking for updates from the Sheriff, to speak to the Sheriff - it was always the same - no response from the Sheriff.
The day the Sheriff finally did an interview was the same day all of the media reported the same thing -
"The FBI had JOINED the case after a week"