Section 38 IPC
38. Persons concerned in criminal act may be guilty of different offences.—Where several persons are engaged or concerned in the commission of a criminal act, they may be guilty of different offences by means of that act.
A attacks Z under such circumstances of grave provocation that his killing of Z would be only culpable homicide not amounting to murder. B, having ill-will towards Z and intending to kill him, and not having been subject to the provocation, assists A in killing Z. Here, though A and B are both engaged in causing Z’s death, B is guilty of murder, and A is guilty only of culpable homicide