In love, engaged, dead

A young student plunges to her death on the day of her engagement in the penthouse of her wealthy father. Was it an accident, or was it a cold-blooded murder? You take on the role of retired detectives. Herbert Kogler, an old acquaintance of yours, has lost his only daughter. He owns the largest and wealthiest real estate company in the city. There are entire neighborhoods in the city center that only house properties owned by him. This includes a luxurious, two-story penthouse where his daughter was planning to celebrate her engagement with her great love on the day of her death. In the middle of the night, she fell down the stairs there and landed fatally. She was dead instantly. Herbert Kogler has asked you to bring some light into the darkness parallel to the police. You naturally want to comply with this request - even though you know it will be anything but easy. You are retired, so you are not actually allowed to officially investigate. If you want to access specialists' reports, you will need to use your contacts.