Harry Potter and the Mystery X Murders

This is a Harry Potter Alternate Universe fanfiction.

Summary : 18 Harry Potter characters are invited to an island. Once there, a typhoon traps them there for 5 days and also cuts off all communication devices. One by one, the 18 Harry Potter characters dies. There are no survivors after 5 days on the island.

You are a detective investigating this case. Find the murderer(s) who is named X. In the end, will you reveal the true face of X?

Hint 1: Every statement in the summary is true.
Hint 2: Every statement enclosed in brackets is true.
Hint 3: Magic does not exist.
Hint 4: Without love, you cannot see the absolute secret.

Well, now that you have everything that you need, will you start investigating this case, Detective?