Who is "O"

[Kedjane]

Neil Oswald probably, there's no mention of anyone else named "O".
Apart from being the chief attending chemist at the water cave I think he was also in charge of security. I can't remember if or where you find his body (is he the one with Greys report, who's blood you drain in the beginning of the game?) but I think he was locked in the same cell as Philip but managed to escape. I think he's the one who wrote all those notes ("watch your step" etc) and made the vents break and so on.