Gotta need to be Stealthy on this one Detective and Thankfully theres not that much secrets to find so lets go find them.
as you investigate the second floor , you will find this room










Look on the side of the small Fireplace and Press the Button , This will open a Secret bookcase and in it you will Find Enough Heat to get rid of goons if things go south.

while searching for clues you will find this bloody handprint










just on the right of it look below the staircase to find tranquilizer gun ammos

in the pool area its on the top of the small wooden roof over a bench , just climb on the hedgerow