A suspect was an individual who the police or the authorities suspected of committing a crime or engaging in criminal activity. The prime suspect was the individual most likely believed to be responsible for a crime. The accused was a suspect charged with a crime or on trial for it. (TOS: "The Conscience of the King", "Court Martial", "Wolf in the Fold")
In Cardassian law, the accused had to prove their innocence. (DS9: "Things Past")
In Human law, the accused was guaranteed the rights of a trial by his peers, representation by counsel, of cross-examination, and of confronting the witnesses against them. These rights were later adopted by the Federation. (TOS: "Court Martial")
In Federation courts, an extradition request for the accused was approved after the legal authorities of a planet or state sufficiently established motive, method, and opportunity. (TNG: "A Matter of Perspective")