I often read and heard about burning tokens that were not sold when the ICO project was finished, I also knew that by burning the rest of the token was a strategy so the price of the token didn't fall, but if the DEV and the team didn't burn it was a crime? is there a requirement that the remaining unsold tokens must be burned?
Its not compulsory to burn tokens left after ICO sales. It's just a strategy introduced to attract customers who will now have the impression that the token circulation will be low and thus translate to high price (according to supply and demand laws). That not withstanding, some projects also lock up such tokens for future marketing and promotion. Which is no big deal