The defence for family axe murder accused Henri van Breda has argued that his police statement is inadmissible.
Advocate Pieter Botha claims the accused's rights were not upheld when he made the statement at the Stellenbosch Police Station following the attack.
The 22-year-old is accused of killing his parents and older brother, and severely wounding his younger sister in their De Zalze home in Stellenbosch in January 2015.
Advocate Pieter Botha says when Van Breda was questioned by police on the morning after the attack, he was made to believe that he was a suspect, which would mean he fell under the protection of Section 35 of the Constitution.
That section includes the right to silence, protection against self-incrimination and the right to legal counsel.
Botha says Van Breda was not told he does not have to make a statement, has the right to consult a lawyer or has the right to remain silent.
He says his client was sleep deprived and had not had anything to eat when he made the statement.
The court has also heard that friends and family were only allowed to give Van Breda clothes and food once he signed the statement.
Prosecutor Susan Galloway has argued Van Breda was not a suspect but a witness at that stage.