Woman have sessions with mute alien male underground prisoner

This is a psychological thriller/scifi (romance?), written in 2010-15 give or take a few years. I think the author is female (since the protagonist is female but I can be wrong).

It's about a woman who gets a job in a secret military facility where I think she has to live in an apartment as well during her time working there. They are very vague with what she's suppose to do before she gets the job. She learns she's going to have sessions with an alien (male) that refuses to communicate with his human captures. She's going to try to study or communicate with him (he is humanoid looking). There's an evil/angry military man (of course) who thinks she's to slow or give to little information. I think she's helping the alien or being cooperative when she learns that she won't be leaving the facilities or her job alive and starts feeling more sympathy than fear for the alien. She doesn't tell military leader man all she learns, withhelding and spoon feeding him information. I think she's having a soft heart and feel for the alien when she see the military taunt/torture him.

The woman discovers the alien male is more intelligent than the military thinks and she learns by the end of the story when he escapes that he can talk (or we get his point of view finally and we "hear" his thoughts as a reader) and he make her hide in one of the workers apartments while he kills a lot of the military men/researchers for a bit (she's afraid he won't make it back to her). I don't remember if we get his point of view here for a bit when he goes on a killing spree or if she listens in on a communication device. He comes back and get her and they escape to ground level with the facility being blown up below them.

I remember for a lot of the time of the book you think the alien is very primitive and dangerous in his behaviour, like a caveman or something (and I think he's naked) and since he doesn't speak and we only have the womans point of view we learn slowly in the same slow speed as the woman about the alien and you're taken by suprise that he's far more intelligent than what he let his human captors believe. I think he has waited there "undercover" for a while, that he has some form of agenda all along but I'm not sure I remember correctly. You get this impression when you learn about his intelligence and his own military like behaviour when they escape near the end of the story.

Appreciate any help! I think I've also read another book with a similar story (but in that book the alien prisoner wasn't so primitive like in the beginning, only refused to talk with his captors and you could tell he was intelligent from the start). I think in that one the romantic feelings between the characters started early on as they could communicate with eachother. In the book I'm actually looking for it's more of a mystery who the prisoner is and what he can do for the bigger part of the book.