Which amendment Protects the rights of the accused?

The Fifth, Sixth, and Eighth Amendments protect the rights of the accused directly.

The Fifth guarantees the right to a grand jury, prohibits double jeopardy (two prosecutions for the same offense), protects against self-incrimination (you don't have to testify against yourself), and guarantees due process of law.

The Sixth guarantees a speedy and public trial, trial by an impartial jury, confrontation of witnesses, and right to counsel (and a few other things not frequently cited).

The Eighth prohibits cruel and unusual punishments, and also excessive bail.

Additionally, two other Amendments apply to accused persons indirectly:

The Fourteenth Amendment applies the Bill of Rights to the States (for the most part).

The Fourth Amendment controls how the police may gather evidence.