Might have been a crime/murder mystery/thriller film or series that I saw sometime between 1987 and 1990, so most likely from the 80s. Was set in the then-present time.
There were either two sisters, or likely twin sisters. One of them is successful, sweet, naive, and good-hearted, and the other is dark, manipulative, grumpy, and somewhat jealous of the other. Both attractive, beautiful women.
Towards the beginning, an attempt is made on the life of the good-hearted sister, although I don’t recall how. She has no known enemies. Luckily, she survives. Everybody is in shock.
The detective investigating the case interviews the victim and the people that know her, including the dark sister. He is somewhat older than the sisters, possibly old enough to be their dad, so I don’t remember there being a romantic attraction. Rather, he tries to protect and watch over the victim.
The detective naturally suspects of the dark sister, but has no proof and cannot see a motive, other than the fact that one sister is obviously more successful and has her life in order and the other does not and is understandably jealous, although her attitude could obviously be much better.
At some point, it is revealed to the viewer that it was the dark sister who attempted to kill her good-hearted sister and now she will try again with a new plan. The dark sister knows that her good-hearted sister has a habit of coming home every night after work and stepping on to the terrace with a drink in her hand and leaning on to the hand rail and enjoying the view to relax. I don’t recall what her exact plan was but it had something to do with loosening the bolts of the hand rail so that when the good-hearted sister leans on the hand rail later that night, she will either fall to her death or the dark sister will let a verbal fight escalate to a point where it would seem “natural” for her to shove her sister towards the hand rail which is now loose…that’s all I remember.