It could be revenge. Maybe someone had a grudge against her and decided to take extreme action.
Possibly, it was for money. Maybe she was involved in something that threatened someone's financial interests. Or, it could be due to a misunderstanding that escalated horribly out of control.
It could be revenge. Maybe someone was wronged in the past and saw murder as a way to get even.
Jealousy is a big one. If a friend has something the other wants, like a better lifestyle or more popularity, it can lead to murder.
One possible motive could be revenge. Maybe the blackmailer felt that the gym teacher had been too strict with them in the past and this was their way of getting back. For example, if the gym teacher had made a student run extra laps for being late, the student might seek revenge through blackmail.
One possible motive is to shock the audience. Horror creators use extreme and disturbing ideas like this to get a strong reaction from people.
Power and control within the family could also be a motive. One sister wife may want to be the dominant figure and see another as an obstacle, so she resorts to murder to assert her authority.
One possible motive could be jealousy. If the innocent person had something that others desired, like a relationship, a job opportunity, or property, it might lead to envy and ultimately murder.
Jealousy can be a big motive. For example, if one student is getting all the attention and good grades, another student might be driven to murder out of envy.
One possible motive could be financial gain, like in the case where a family member wants to inherit money or property. For example, if a person is in debt, they might think murdering other family members who stand in the way of the inheritance will solve their problems.
Possible motives could include revenge. If someone felt wronged in the past, they might seek vengeance through murder.
One possible motive could be greed. For example, if a player has a lot of valuable items or gold, other players might murder them to steal those possessions. Another motive could be revenge. If two players or guilds have a feud, they may target each other's members for murder. Jealousy can also be a motive, like when a player is jealous of another's achievements or status in the game.