a. Co-defendants as witnesses
For the co-defendants
Section 54(1) of the Criminal Procedure Ordinance (Cap. 221) provides that a defendant in criminal proceedings is competent only as a witness for the defence (i.e. himself or co-defendants).
If the defendant chooses to provide testimony for a co-defendant, he will also open himself up to cross-examination by the prosecution regarding his own guilt, including his own involvement in the offence.
For the prosecution
However, in a case involving more than one defendant, there are a number of ways in which an accused might be competent to give evidence for the prosecution.
If the co-defendant ceases to be a “person charged”, he or she would be a competent prosecution witness. Also, if a co-defendant had pleaded guilty and upon his or her conviction, he or she would be a competent and compellable witness for the prosecution or other co-defendants. If one or more co-defendants are severed from the proceedings, they cease to be in the same proceedings, and are therefore competent and compellable witnesses.