The case for the Crown against the four co-accused, who
were charged with manslaughter and aggravated assault, was
that each was guilty as an aider, an abettor, or a participant in
a common unlawful purpose under s. 21(2) in pursuit of which
the offences charged were committed.
 In a portion of the charge headed “Modes of Participation”,
the trial judge gave general instructions about each mode of participation in an offence that s. 21 describes:
— common purpose.
In his discussion of liability as a principal, the trial judge said:
Sinhem Srun is charged alone with the second degree murder of Vandin Svay
and attempted murder of Mao Kim. He can only be a principal participant in
 After he had provided general instructions about aiding
and abetting, which he said were only applicable to the counts
charging manslaughter and aggravated assault, and thus did not
apply to the appellant, the judge turned to s. 21(2) and concluded:
“This applies to all counts.”
 The trial judge then expanded somewhat on his instruc-
tions on aiding and abetting before he returned to some addi-
tional directions on s. 21(2). This time, he told the jury that
the instructions on s. 21(2) applied only to the counts of
manslaughter and aggravated assault — counts two and four in
the indictment — with which the appellant was not charged.
These instructions contained no reference to the counts of
murder and attempted murder or to the appellant.
 In his instructions on count one, in which the appellant
alone was charged with second degree murder, the trial judge
described the essential elements of the offence in a series of three
questions. After accurately reviewing the mental elements in
s. 229(a), the trial judge continued:
With murder, the person must have actual knowledge to his satisfaction that
another in the group would likely continue the acts of assaulting Mr. Svay to
the point of causing death. Subjective means that the defendant had to know;
in this case, Mr. Srun. And he is alleged to be the principal.
 The trial judge then explained to the jury how they could
determine the appellant’s state of mind from the evidence
adduced at trial: