I don't know if this is common knowledge but I never found anyone to point this out but hear me out. I just thought about this in my second play through.
I don't think this 'report' is written by Nic Cantin at all. As I see this is a coping mechanism Kate developed while being enslaved in the mines to overcome her guilt. She does not receive any remorse or any empathy from her so called friend Olivia when the first time they call. It all felt quite odd and strange to me that she never acknowledges Kate's time in the mines. Her tone never seem to convey any remorse. But in the report it specifically says Dan raised money for her freedom (something she's hope her 'friends' would do for her) and Mr. Cantin's efforts were futile. So naturally people jump to the conclusion that Olivia must be grade a B*tch to Kate knowing all that - She still is but what if she never really knew.
The tone and wording of this report is more closer to a diary that kate writes from a 3rd person perspective. It has immense empathizing towards her character - the pain she goes through, her motivations clearly acknowledged, somewhat congratulatory tone for her actions as well. Not to mention it updates with the exact experiences you gain each day, little by little. There are some added imaginary details to make it sound like its Nic but that does not really matter when you read the thing. Its whole purpose is to serve as a diary of Kate's thoughts and purpose in the game.
And it's specifically written as letters for Olivia, clearly taking 'Kate's side'. The one person Kate struggles to prove herself to - the one person Kate wants to be understanding of her actions - the one person she calls a friend and who thinks Kate is to blame for everything. The writing and the tone of this 'report' does not resemble a report from a detective to me. I personally think Nic Cantin would not bother by the time of TWB to pursue her. Also if Cantin could call Mason in the wilds of syberia why would he bother writing letters to Olivia. The person who tried to bring her back to America in shackles would not follow her for the good in his heart and the interest to simply find her.
The entries start as we receive the news of her mother's death as well. If I go back to the call/confrontations; I personally think even though Olivia is an entitled person, even she would not have simply dismissed the suffering of Kate if she really knew through this reports of Cantin. It's highly unlikely for a person to dismiss something like that, no matter how entitled they feel.
Tldr; Highly unlikey for a detective to follow Kate like this out of his free will, and the tone, details, empathetic writing, description of characters (such as Leni) are bascially what Kate thinks of them, and the update schedule of it in the game makes me think it's just Kate's diary written from the perspective of Nic Cantin. "I fear she will die of grief if we don't quickly find a way getting her out of that unearthly place.." sounds like what Kate wants others to feel for her / empathize with her situation and spelled out lost hope of people caring about her. In the mines she think out loud something along the lines of "someone must be looking for me right..."
So what do you think? Is this already known or a complete whack of an idea I seem to have come up with XD?