MOO follow:
Points to ponder and possibilities in order of expected likelihood of what occurs in a disappearance case given similar circumstances:
1) The person who reported there is a person missing is asked the who, when, where and what of the situation.
2) The last person to see the missing person is questioned by LE regarding what they were doing, where, when, duration, what was done prior and where they were heading and did any/all of that involve with the missing person. In this case, the same person who reported the missing person is also the last person to have seen them.
3) A significant other is questioned for research purposes during initial investigation. In this case, the SO is person who reported the person as being missing, also is the last person to have seen the missing person and also is the last person to have been directly involved in activities with the missing person.
4) LE follows where the initial information takes them, while also maintaining possibilities based against statistics and experience:
a) a missing person may have 'disappeared' on purpose or accidentally (forgot to tell someone they were going somewhere or doing something).
b) a missing person may have encountered an issue like having become disoriented, confused, lost or had an accident such as, fell into a mine shaft, a well, a rock formation crevice (any of which might prevent others from easily locating them).
c) the last person with the missing person may become a person of interest based on if initial information does not encompass logic of the situation/scenario.
d)same as the above except the person is a significant other or other family member.
e) foul play such as kidnapping, abduction and/or murder.
What do we have with this case?
The SO reported BT missing.
The SO is the last person to have seen BT.
The SO is the last person to have been directly involved in activities with BT.
The SO provided information that appears to encompass logic of the situation/scenario.
I am not sure (beyond the SO reporting LE 'told' them they were deceptive in their polygraph testing) what the situation-reporter/last person/SO has said or done that would make LE suspicious of their character (not "characters" plural because all of those persons are the same person) regarding this case.
IMO, with RT being all of those people (reported it, last person seen with/activities with/SO) it makes the situation appear suspicious but, without evidence to bolster that suspicion LE must consider all possibilities beyond the statistical "the spouse did it" scenario.
We are not privy to all information LE has gathered and even with a VI providing their own input we have no solid basis on which to come to any conclusions.
IOW, at this stage in the investigation, with no evidence (AFAIK) of RT having committed a crime, an abduction situation is likely.
OTOH, the needle on my hinky meter is not laying across the zero mark...........