What Alice Saw There
An amateur painter stops by home after work and is killed inside her bedroom. Both exits were being watched by her four friends, yet none of them spotted the killer.
This is my first gameboard, expect the difficulty level to be low.
Rules
Alright let me explain what went down here.
1.) The red truth said Catherine and Edward could not see any way out other than the door and the balcony door.
2.) This leaves room for things they failed to see.
3.) There are paintings of any size in the room. Those could conceal another door. Alternatively, if the door counts as an object that has to be mentioned, the door itself could have been painted on to make it not look like a door.
4.) It was their first time inside the room, so they wouldn't be aware of what the layout was supposed to be.
5.) Alice went into the room with intention to get dressed.
6.) She was explicitly still wearing the same clothes when found and no other clothes were inside the room.
7.) Makes sense if there was actually a closet or bathroom connected to the bedroom though.
8.) Bertrand realized this because he's been there before and went back to get shot by the killer. 
So yeah.
Hidden passage.
@Blackrune
Well played!
The culprit was a burglar who entered through the balcony door and later hid in the closet when he heard Catherine's car arriving.
When Alice opened the closet door to get her clothes she was shot and pushed to the middle of the room. The culprit then hid in the closet, using a painting to cover the closet door.
Bertrand figured out the truth once he realized that there were no clothes in the room besides the one she had been wearing.
