Can one be punished only based on confession?

Very short answer:
Yes—but only if it is a voluntary, truthful judicial confession recorded lawfully before a Magistrate. Police-obtained or coerced confessions cannot be used. And a co-accused’s confession cannot, by itself, convict another.

The legal position (Bangladesh)

1. Admissible confessions vs. inadmissible confessions

• Judicial confession (before a Magistrate):
  If recorded under Section 164, Code of Criminal Procedure, 1898 (CrPC) with all safeguards, it is substantive evidence and can, in law, be the sole basis of conviction if the court believes it is voluntary and true.
  Supporting provisions: Evidence Act, 1872, s.24–30; CrPC, s.164; constitutional bar on compulsion: Art. 35(4), Constitution.
• Confession to police officer: Inadmissible: Evidence Act, s.25.
• Confession while in police custody (not in Magistrate’s presence): Inadmissible: Evidence Act, s.26.
• Discovery exception: Only the fact discovered portion is admissible: Evidence Act, s.27.

1. When a confession alone can convict

• A properly recorded judicial confession (s.164 CrPC), found by the court to be voluntary, reliable and truthful, may by itself sustain a conviction.
• Corroboration is a rule of prudence, not of law: courts often look for some assurance (e.g., medical or circumstantial consistency), especially if the confession is later retracted, but they can convict on the confession alone if they are fully satisfied.

1. Co-accused confessions

• A confession by one accused cannot be the sole basis to convict another accused; it can only be “taken into consideration” along with other evidence: Evidence Act, s.30.

1. Safeguards the Magistrate must ensure (s.164 CrPC)

• Clear warning that the maker is not bound to confess and that it may be used against them.
• The Magistrate must satisfy himself that the confession is being made voluntarily, free from inducement, threat or promise (Evidence Act, s.24), and free from police influence (often giving time for reflection and ensuring the maker is out of police custody before recording).
• The confession must be recorded and signed, with the Magistrate’s certificate as to voluntariness (Evidence Act s.80 presumption for judicial records may apply).

1. Retracted confessions

• If an accused retracts a judicial confession, courts treat it with great caution; typically they seek some corroboration in material particulars before acting on it. However, a retracted but otherwise credible judicial confession can still ground a conviction if the court is convinced it was true when made.

Takeaway

• Yes, punishment can be based solely on a confession—but only where it is a judicial confession recorded per s.164 CrPC, and the court finds it voluntary and true.
• No, if it is a police confession (s.25) or a custodial confession not made before a Magistrate (s.26).
• No, for a co-accused’s confession standing alone (s.30)—you need independent evidence against the other accused.
• Prudence: courts prefer corroboration, especially for retracted confessions, but it is not a hard-and-fast legal requirement for a properly recorded judicial confession.