Great question. It will be any upper caste who are above Dalits. There is no one perpetrator here but all of them. The main point to note is that the caste hierarchy is sacred and will be enforced by endogamy (arranged marriages) and other occupational rules.

You will be shown your place very very quickly. Love marriages are quite deadly and parents killing their own children and the lower caste grooms are extremely common. You can search for "honour killings in India".

Please read "Annihilation of Caste" by Dr. B.R. Ambedkar. Its around 50 pages of an undelivered speech, later published.

If you want to learn about caste, please make sure not to ask for explanations from an upper caste person. This is extremely important!!

Example of this enforcement: https://www.bbc.com/news/world-asia-india-15997648