I suppose the concept of double jeopardy to you is watching two episodes of Jeopardy! back to back....
Unfortunately for you, what you want is plainly illegal in South Africa.
https://www.gov.za/documents/constitution/chapter-2-bill-rights#35
If the state wants murder and assault charges, then that is what he will go to court for. If he is found innocent of those charges, the state cannot say: well he is innocent of murder, but we will now bring a charge of culpable homicide against him instead. The state has one trial to find him guilty of murder and assault. If they don't succeed with that, it is over.