A lot of people had problems with this, so you're not alone. In the hallway, there is a splatter of blood on the floor near where Eva is standing. It's very easy to miss, and the game does nothing to point you toward its existence.

To the developers, I suggest one of the following fixes:
1.) Make the bloodstain outside the boiler room much more apparent. As is, it blends into the environment too well, and you don't have access to the Detective View feature in 3D walking sections.

2.) If you finish investigating the four storage rooms before finding the bloodstain outside the boiler room, instead of telling you to go upstairs, Eva should tell you to investigate the hallway again, and if you talk to her, she should have a new set of dialogue where she directs the player to look at the blood on the floor.