What was unfair about Charles 1 trial?

Charles I's trial in 1649 was considered unfair due to several factors, including the lack of a legitimate legal framework, as he was tried by a court established by Parliament without the King's consent. The trial was characterized by a predetermined outcome, with many judges already opposed to the monarchy. Additionally, Charles was denied the right to present a proper defense, and he was not allowed to appeal the proceedings, undermining the principles of justice and due process.