I think it is highly possible that Hans Nieman did not cheat......and is an emerging chess genius. Magnus only played him once and lost. Because Nieman is lowly ranked he is accused.
These are my observations and reasoning in why Hans may not have cheated
1. Computers standard of play is very high and at God level no human can come close. If he cheated using computer he will sweep through there tournament easily.
2. But analysing the games he played and lost against eventual winner. He is actually very good and lost narrowly. It means his actual strength is much higher than his rank.
3. Look at the games he won, it is also very long drawn with human mistakes. If he cheated using a computer he would have easily demolished the opponent with obscure lines that only computer can find.
4. My believe is he is a player who improved very quickly going into his late teens something common among chess prodigies. He did not actively play in tournament to improve ranking.
5. When he played Carlson, Carlson expected an easy win but lost. As world champion he could not accept a lowly player beating him. His ego shattered he resorted to cheating accusation.
6. For live tornament it is not easily to cheat. You need to hide a computer on your body or communicate with it remotely to give the moves to analyse. Or use an accomplice who input the moves then transmit the analysis to you. It can be done but very hard.