Well, it could be that he has a long criminal record and has been involved in various illegal activities like theft, fraud, and assault. Maybe he was part of a criminal gang that was into multiple kinds of crimes.
He will likely go through the legal process. First, he'll be booked at the police station, which includes having his information recorded, fingerprints taken, etc. Then he'll probably have to appear in court. If he can't afford a lawyer, one will be appointed for him.
One possible reason could be excessive stress. When a man is under a great deal of stress, his mind might be so preoccupied that he forgets things easily. Another reason could be a lack of proper sleep. Without enough sleep, the brain doesn't function well and memory can be affected. Also, it might be due to some nutritional deficiencies, for example, not getting enough B - vitamins which are important for brain health.
In fanfiction, the Dursleys could get arrested for child abuse. They treated Harry Potter horribly, locking him in a cupboard, underfeeding him, and constantly berating him. Another reason might be for illegal use of magic items. If they got hold of some magical objects through Harry and misused them, that could lead to their arrest.
One possible reason could be drugs. If he was involved in a large - scale drug - trafficking operation, that would be quite epic and lead to his arrest.
One possible reason could be that the original Naruto story has a very distinct and carefully crafted world and character arcs. Fanfiction might distort these in ways that seem disrespectful to the source material, making Naruto, as a character concept, seem to 'hate' it. For example, some fanfictions may change Naruto's core values or relationships in a way that goes against the essence of the character.
It could be a hard and challenging one. He might have to start from scratch, face lots of difficulties, and find the strength to rebuild his life.
One possible reason could be a misunderstanding. Maybe some dark magic was involved that made Harry believe the Weasleys were acting against him or the wizarding world in a way that seemed illegal. For example, if there was a spell that distorted his perception of their actions.
There are various possibilities. He might have a sudden stroke of luck and get back on his feet. Another option is that he leans on the support of friends and family to slowly regain what he's lost. Sometimes, though, people in such a situation struggle for a long time before seeing any improvement.
It might be because of her anti - Muggle - born policies. Fanfiction often explores the idea that Harry discovers Umbridge's discriminatory plans against Muggle - borns. This is completely against the values of the wizarding world, and Harry, having Muggle - born friends, would take steps to expose her and get her arrested for such bigotry.
It could be due to a mental breakdown. For example, if he had been under a great deal of stress for a long time, perhaps from work or family pressures, and suddenly couldn't take it anymore. Or he might have some undiagnosed mental illness that led him to this extreme action. Also, a sudden and tragic event in his life like the loss of a loved one could be a reason.