This is one of the side cases, which you can solve in Observer. You can unlock it after completing the initial part of the game, that is after investigating the crime scene in apartment 007 and leaving it. That will unlock access to a large portion of the block of flats.
For the case in discussion you must head to the building’s first floor and reach apartment 113 (use the maps on the walls if you have troubles reaching that place). Interact with the intercom there in order to talk to a girl named Paulina. Paulina gives you the code 1074, which results in adding the case to the main hero’s journal.
You do not have to look far to find the place where you can use Paulina’s code – the code panel is by the door to the neighboring apartment 114. Interact with it and input the code 1074.
In the first room you will find a picture (secret) and some objects to scan: a holo-frame and inhaler (use the Bio Vision on that). Move the curtain and step into the next room. The most important finding is the one shown in the picture above – the woman wired to a complex machine. Scan the device and the woman. You will also find synchrozine syringes nearby, a computer (you can look through its disk) and the syringe with the substance 45F.