I'm talking about the movie The Conjuring: The Devil Made Me Do It
In the latest edition of Conjuring franchise, we get to see that a boy murders someone and then constantly tries to commit suicide. Later, we find that it had happened before. A girl murdered another girl and then committed suicide.
Now, who's behind all this? A daughter of a priest, who is an occultist. She practises black magic and casts spells on people. She cast a curse on David Glatzel, which later transferred to Arne. This curse has a unique signature. A person is murdered and the murderer commits suicide. Ed and Lorraine found two cases and mentioned there must be a connection between two victims.
Unfortunately, the reason was never established. Or I may have missed it. How is the priest's daughter connected to David and Jessica? What was her motive to cast a curse on them? How are these victims connected?