As we don't have the actual facts about the 'gilbert killing three kids story', we can only hypothesize about motives. It might be that Gilbert was in a desperate situation in his own life and took out his frustration on the innocent kids. Or there could be some sort of delusion in his mind that made him think harming the kids was necessary. Without proper details, we can't be certain at all.
Since I don't know the details of this story, it's hard to say the motives. It could be due to mental illness, or some personal grudges against the families of the kids. But this is just speculation without more information.
Not having the full story makes it tough to determine motives. However, in general, motives for such a heinous act could range from a desire for revenge, perhaps if Gilbert felt wronged by someone related to the kids. Another possibility could be some form of psychological breakdown where he was unable to control his violent impulses. But again, this is all just guesswork.
There are unfortunately many stories of violence in the world. If this 'gilbert killing three kids story' is a real event, it must be a tragic and horrifying one. But since I have no information about it, it's impossible to provide more details. It might be a story from a particular community, or it could be something that was reported in a very limited scope.
Mental illness. Just like anywhere else, small towns can have individuals with mental health issues that may lead them to commit a killing, perhaps due to hallucinations or uncontrollable impulses.
Jealousy could be one motive. They might be jealous of Harry's special status as a wizard. They see him as different and a threat to their 'normal' family life, so they want to get rid of him.
It could be that she was lonely. Living alone in that house, she saw the kids as a way to have some company, though her way of inviting them was very wrong and dangerous.
One possible motive could be Anakin's fall to the dark side. The dark side clouds his judgment and makes him see Obi - Wan as an obstacle to his power. He might believe that by eliminating Obi - Wan, he can fully embrace the dark side and gain more control. Another motive could be jealousy. If Anakin feels that Obi - Wan is always favored or is holding him back in some way, this could fuel his anger and lead to him wanting to kill Obi - Wan. Also, the influence of Palpatine might play a huge role. Palpatine could have manipulated Anakin into believing that Obi - Wan is a threat to the new order he wants to create.
One possible motive could be a conflict over their loyalties. Remus is a werewolf and has his own set of insecurities and allegiances. Maybe Snape discovers something about Remus that he threatens to expose, leading Remus to kill him in a moment of panic. For example, if Snape were to find out about Remus endangering students during his werewolf transformations and was about to report him to the authorities.
One possible theme could be love against all odds. Maybe they faced family opposition or social barriers.
One possible motive could be that Mewtwo sees Ash as a threat to its own power or freedom. Ash is constantly on a journey to catch and train Pokémon, and Mewtwo, being a powerful and intelligent Pokémon, might view Ash's actions as a potential danger to its kind or its own existence.
It could be a form of exploring darker themes. The writer might be interested in how the RWBY world would react if Ruby Rose was killed. They might want to see how other characters would develop or change in the face of such a tragedy. However, this is a rather extreme way of exploring those themes and might not be well - received by most fans.
It could be revenge. Maybe one character was wronged and sought justice through killing.